Sub-channel allocation in orthogonal frequency division multiplex wlan

ABSTRACT

A method for simultaneous communication with multiple communication devices in a wireless local area network is described. Respective sub-channels of an orthogonal frequency division multiplexing (OFDM) communication channel are allocated to two or more second communication devices for simultaneous OFDM transmission to the two or more second communication devices, including allocating first and second sub-channels to first and second ones of the two or more second communication devices, respectively. Respective downlink OFDM data units are generated using the corresponding allocated sub-channels. The downlink OFDM data units are transmitted using the corresponding allocated sub-channels. At least first and second uplink OFDM data units transmitted by the respective second communication device in response to the corresponding downlink OFDM data unit are received. The first and second uplink OFDM data units are transmitted from the respective second communication device via the corresponding allocated sub-channel.

CROSS-REFERENCE TO RELATED APPLICATION

This disclosure claims the benefit of U.S. Provisional PatentApplication No. 62/011,332, entitled “Bandwidth/AC Selection andAcknowledge Indication in OFDMA, UL MU MIMO” and filed on Jun. 12, 2014,U.S. Provisional Patent Application No. 62/044,838, entitled“Bandwidth/AC Selection and Acknowledge Indication in OFDMA, UL MU MIMO”and filed on Sep. 2, 2014, and U.S. Provisional Patent Application No.62/112,959, entitled “Bandwidth Selection and Acknowledge Indication inOFDMA, UL MU MIMO” and filed on Feb. 6, 2015, the disclosures of each ofwhich are incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughputs, such as throughputs in the tens of Gbps range.

These WLANs operate in either a unicast mode or a multicast mode. In theunicast mode, the AP transmits information to one client station at atime. In the multicast mode, the same information is transmitted to agroup of client stations concurrently.

SUMMARY

In an embodiment, a method for simultaneous communication with multiplecommunication devices in a wireless local area network includesallocating, by a first communication device, respective sub-channels ofan orthogonal frequency division multiplexing (OFDM) communicationchannel to two or more second communication devices for simultaneousOFDM transmission to the two or more second communication devices,including allocating a first sub-channel to a first one of the two ormore second communication devices and a second sub-channel to a secondone of the two or more second communication devices. The method alsoincludes generating, by the first communication device, respectivedownlink OFDM data units for the two or more second communicationdevices using the corresponding allocated sub-channels. The methodincludes transmitting, by the first communication device, the downlinkOFDM data units to the two or more second communication devices usingthe corresponding allocated sub-channels. The method also includesreceiving, at the first communication device, at least i) a first uplinkOFDM data unit transmitted by the first one of the two or more secondcommunication devices in response to the corresponding downlink OFDMdata unit and ii) a second uplink OFDM data unit transmitted by thesecond one of the two or more second communication devices in responseto the corresponding downlink OFDM data unit, wherein the first uplinkOFDM data unit is transmitted from the first one of the two or moresecond communication devices via the first sub-channel allocated to thefirst one of the two or more second communication devices and the seconduplink OFDM data unit is transmitted from the second one of the two ormore second communication devices via the second sub-channel allocatedto the second one of the two or more second communication devices.

In another embodiment, a method for simultaneous communication withmultiple communication devices in a wireless local area network includesreceiving, at a first communication device from a second communicationdevice, a downlink orthogonal frequency division multiplexing (OFDM)data unit via an OFDM communication channel. The method also includesidentifying, by the first communication device, a sub-channel of theOFDM communication channel on which the downlink OFDM data unit wastransmitted by the second communication device. The method includesgenerating, by the first communication device in response to thedownlink OFDM data unit, an uplink OFDM data unit to be transmitted viathe sub-channel on which the downlink OFDM data unit was transmitted.The method also includes automatically transmitting the uplink OFDM dataunit to the second communication device via the sub-channel on which thedownlink OFDM data unit was transmitted.

In an embodiment, a method for simultaneous communication with multiplecommunication devices in a wireless local area network includesreceiving, at a first communication device, one or more downlinkorthogonal frequency division multiplexing (OFDM) data units transmittedby a second communication device via one or more respective sub-channelsof an OFDM communication channel. The method includes identifying, bythe first communication device, the one or more sub-channels of the OFDMcommunication channel on which the one or more downlink OFDMA data unitswere transmitted. The method also includes determining, by the firstcommunication device, whether each of the one or more sub-channels onwhich the one or more downlink OFDMA data units were transmitted isbusy. The method includes generating, by the first communication device,an uplink OFDM data unit for each sub-channel determined to be not busy.The method also includes transmitting each of the uplink OFDM data unitsto the second communication device via the corresponding sub-channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN), according to an embodiment.

FIGS. 2A, 2B, and 2C are diagrams illustrating example orthogonalfrequency division multiplexing (OFDM) sub-channel blocks for an 80 MHzcommunication channel, according to an embodiment.

FIG. 3 is a diagram of an example orthogonal frequency division multipleaccess (OFDMA) data unit, according to an embodiment.

FIG. 4 is a diagram of an example OFDMA data unit, according to anotherembodiment.

FIG. 5 is an example broadcast block acknowledgment field, according toan embodiment.

FIG. 6 is diagram illustrating a frame exchange between an AP andmultiple client stations, according to an embodiment.

FIG. 7 is a diagram illustrating various acknowledgment types for atransmission opportunity holder, according to an embodiment.

FIG. 8 is a diagram illustrating a block acknowledgment during a frameexchange for a TXOP holder, according to an embodiment.

FIG. 9 is a frame exchange between an AP and a plurality of clientstations that includes an uplink transmission of data from the pluralityclient stations to the AP, according to an embodiment.

FIG. 10 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.

FIG. 11 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.

FIG. 12 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.

FIG. 13 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment.

FIG. 14 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment.

FIG. 15 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment.

FIG. 16 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to another embodiment.

FIG. 17 is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to an embodiment.

FIG. 18 is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to an embodiment.

FIG. 19 is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to an embodiment.

FIG. 20 is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to an embodiment.

FIG. 21 is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to an embodiment.

FIG. 22 is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data with selectedtraffic identifiers, according to an embodiment.

FIG. 23 is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data with selectedtraffic identifiers, according to an embodiment.

FIG. 24 is a frame exchange between an AP and a plurality of clientstations that includes both uplink OFDMA transmission of data anddownlink OFDMA transmission of data with selected traffic identifiers,according to an embodiment.

FIG. 25 is a diagram illustrating example uplink OFDMA parameters for anOFDMA group of client stations, and communications between an AP andclient stations of the OFDMA group that occur during time periodsdefined by the OFDMA parameters, according to an embodiment.

FIG. 26 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to an embodiment.

FIG. 27 is a flow diagram of another example method that is implementedby an AP in a WLAN, according to another embodiment.

FIG. 28 is a flow diagram of an example method for simultaneouscommunication with multiple communication devices in a wireless localarea network, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) simultaneouslytransmits independent data streams to multiple client stations and/orreceives independent data streams simultaneously transmitted by multipleclient stations. In particular, the AP transmits data for the multipleclients in different sub-channels of an orthogonal frequency divisionmultiplexing (OFDM) communication channel, in various embodiments. In anembodiment, the sub-channels indicate bandwidth in an orthogonalfrequency division multiple access (OFDMA) transmission, in anembodiment. In another embodiment, the sub-channels are space timestreams of a multiuser multiple input, multiple output (MU-MIMO)communication channel. Similarly, multiple client stationssimultaneously transmit data to the AP, in particular, each clientstation transmits data in a different OFDM sub-channel, in variousembodiments.

The AP is configured to operate with client stations according to atleast a first communication protocol. The first communication protocolis sometimes referred to herein as “high efficiency WiFi,” “highefficiency WLAN,” “HEW” communication protocol, or 802.11axcommunication protocol. In an embodiment, the first communicationprotocol supports OFDMA communication between the AP and the clientstations. In an embodiment, the first communication protocol supportsMU-MIMO communication between the AP and the client stations. In someembodiments, different client stations in the vicinity of the AP areconfigured to operate according to one or more other communicationprotocols that define operation in the same frequency band as the HEWcommunication protocol but with generally lower data throughputs. Thelower data throughput communication protocols (e.g., IEEE 802.11a, IEEE802.11n, and/or IEEE 802.11ac) are collectively referred herein as“legacy” communication protocols. The legacy communication protocols donot support OFDMA communication, in an embodiment. In anotherembodiment, the legacy communication protocols do not support MU-MIMOcommunication.

In an embodiment, client stations that are configured to operateaccording to the HEW communication protocol generally support OFDMAcommunication and/or MU-MIMO communication initiated by the AP. In someembodiments, client stations that are configured to operate according tothe HEW communication protocol optionally support OFDMA communicationand/or MU-MIMO communication initiated by the client stations.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 includes differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 includesdifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. Two or more of the client stations 25are configured to receive corresponding data streams that aretransmitted simultaneously by the AP 14. Additionally, two or more ofthe client stations 25 are configured to transmit corresponding datastreams to the AP 14 such that the AP 14 simultaneously receives thedata streams.

A client station 25-1 includes a host processor 26 coupled to a networkinterface 27. The network interface 27 includes a MAC processing unit 28and a PHY processing unit 29. The PHY processing unit 29 includes aplurality of transceivers 30, and the transceivers 30 are coupled to aplurality of antennas 34. Although three transceivers 30 and threeantennas 34 are illustrated in FIG. 1, the client station 25-1 includesdifferent numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 30 andantennas 34 in other embodiments.

In an embodiment, one or more of the client stations 25-2, 25-3, and25-4 has a structure the same as or similar to the client station 25-1.In these embodiments, the client stations 25 structured like the clientstation 25-1 have the same or a different number of transceivers andantennas. For example, the client station 25-2 has only two transceiversand two antennas (not shown), according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation that is not enabled to receive a data stream that issimultaneously transmitted by the AP 14 with other independent datastreams as part of an OFDMA transmission or as part of a MU-MIMOtransmission to multiple client stations 25. Similarly, according to anembodiment, the legacy client station 25-4 is not enabled to transmit adata stream that to the AP 14 as part of OFDMA transmission or as partof a MU-MIMO transmission from multiple client stations 25. According toan embodiment, the legacy client station 25-4 includes a PHY processingunit that is generally capable of receiving a data stream that issimultaneously transmitted by the AP 14 with other independent datastreams that are intended for other client stations 25. But the legacyclient station 25-4 includes a MAC processing unit that is not enabledwith MAC layer functions that support receiving the data stream that issimultaneously transmitted by the AP 14 with other independent datastreams that are intended for other client stations 25. According to anembodiment, the legacy client station 25-4 includes a PHY processingunit that is generally capable of transmitting a data stream to the AP14 at the same time that other client stations 25 transmit data to theAP 14. But the legacy client station 25-4 includes a MAC processing unitthat is not enabled with MAC layer functions that support transmitting adata stream to the AP 14 at the same time that other client stations 25transmit data to the AP 14.

In an embodiment, the AP 14 and the client stations 25 contend forcommunication medium using carrier sense multiple access with collisionavoidance (CSMA/CA) protocol or another suitable medium access protocol.Further, in an embodiment, the AP 14 or a client station 25 dynamicallyselects a bandwidth for a transmission based on channels available forthe transmission. In an embodiment, communication between the AP 14 anda legacy client station (e.g., the legacy client station 25-4) occur ina primary channel of the WLAN 10, or in a wider channel that includesthe primary channel of the WLAN 10. For example, the legacycommunication protocol requires that each transmission includes theprimary channel, in an embodiment. On the other hand, communicationbetween the AP 14 and a non-legacy client station 25 (e.g., the clientstation 25-1) can occur in one or more communication channels that donot include the primary channel, in an embodiment. For example, thenon-legacy communication protocol, such as the HEW communicationprotocol, allows communication between the AP and the client stations tooccur in a communication channel that does not include the primarychannel, in an embodiment.

In an embodiment, the AP 14 is configured to simultaneously transmitdifferent OFDM units to different client stations 25 by forming an OFDMAdata unit that includes the different OFDM data units modulated inrespective sub-channel blocks of the OFDMA data unit. In an embodiment,the AP 14 allocates different sub-channels to different client stationsand forms the OFDMA data unit that includes OFDM data units directed toby modulating the different client stations in sub-channel blockscorresponding to the sub-channels assigned to the client stations. In anembodiment, when the one or more client stations include a legacy clientstation, the AP assigns a channel that includes a primary channel of theWLAN 10 to the legacy client station, and assigns one or morenon-primary communication channels of the WLAN 10 to one or morenon-legacy client stations. When the one or more client stations do notinclude any legacy client stations, the AP assigns the primary and thenon-primary communication channels in any suitable manner to the one ormore client stations, in various embodiments.

In an embodiment, the AP 14 is configured to simultaneously transmitdifferent OFDM units to different client stations 25 by transmitting thedifferent OFDM data units via different space time streams of a MU-MIMOcommunication channel. In an embodiment, the AP 14 allocates differentsub-channels (i.e., space time streams) to different client stations andforms the OFDM data units and modulates the different OFDM data units tothe space time streams corresponding to the sub-channels assigned to theclient stations. In an embodiment, when the one or more client stationsinclude a legacy client station, the AP assigns a channel that includesa primary channel of the WLAN 10 to the legacy client station, andassigns one or more non-primary communication channels of the WLAN 10 toone or more non-legacy client stations. When the one or more clientstations do not include any legacy client stations, the AP assigns theprimary and the non-primary communication channels in any suitablemanner to the one or more client stations, in various embodiments.

FIGS. 2A, 2B, and 2C are diagrams illustrating example OFDM sub-channelblocks for an 80 MHz communication channel, according to an embodiment.In FIG. 2A, the communication channel is partitioned into fourcontiguous OFDM sub-channel blocks, each having a bandwidth of 20 MHz.The OFDM sub-channel blocks include independent data streams for fourclient stations. In FIG. 2B, the communication channel is partitionedinto two contiguous OFDM sub-channel blocks, each having a bandwidth of40 MHz. The OFDM sub-channel blocks include independent data streams fortwo client stations. In FIG. 2C, the communication channel ispartitioned into three contiguous OFDM sub-channel blocks. Two OFDMsub-channel blocks each have a bandwidth of 20 MHz. The remaining OFDMsub-channel block has a bandwidth of 40 MHz. The OFDM sub-channel blocksinclude independent data streams for three client stations. In someembodiments, a sub-channel has a bandwidth that is less than 20 MHz, forexample, 10 MHz, 2 MHz, or another suitable bandwidth.

Although in FIGS. 2A, 2B, and 2C, the OFDM sub-channel blocks arecontiguous across the communication channel, in other embodiments theOFDM sub-channel blocks are not contiguous across the communicationchannel (i.e., there are one or more gaps between the OFDM sub-channelblocks). In an embodiment, each gap is at least as wide as one of theOFDM sub-channel blocks. In another embodiment, at least one gap is lessthan the bandwidth of an OFDM sub-channel block. In another embodiment,at least one gap is at least as wide as 1 MHz. In an embodiment,different OFDM sub-channel blocks are transmitted in different channelsdefined by the IEEE 802.11a and/or 802.11n Standards. In one embodiment,the AP includes a plurality of radios and different OFDM sub-channelblocks are transmitted using different radios.

FIG. 3 is a diagram of an example OFDMA data unit 300, according to anembodiment. The OFDMA data unit 300 includes a plurality of OFDM dataunit 302-1, 302-2 and 302-3. In an embodiment, the AP 14 transmits theOFDM data units 302-1, 302-2, 302-3 to different client stations 25 viarespective OFDM sub-channels within the OFDMA data unit 300. In anotherembodiment, different client stations 25 transmit respective OFDM dataunits 302-1, 302-2, 302-3 to the AP 14 in respective OFDM sub-channelswithin the OFDMA data unit 300. In this embodiment, The AP 14 receivesthe OFDM data units 302-1, 302-2, 302-3 from the client stations 25 viarespective OFDM sub-channels of within the OFDMA data unit 300, in thisembodiment.

Each of the OFDM data units 302-1, 302-2, 302-3 conforms to acommunication protocol that defines OFDMA communication, such as the HEWcommunication protocol, in an embodiment. In an embodiment in which theOFDMA data unit 300 corresponds to a downlink OFDMA data unit, the OFDMAdata unit 300 is generated by the AP 14 such that each OFDM data unit302 is transmitted to a respective client station 25 via a respectivesub-channel of the WLAN 10 allocated for downlink transmission of theOFDMA data unit 300 to the client station. Similarly, an embodiment inwhich the OFDMA data unit 300 corresponds to an uplink OFDMA data unit,the AP 14 receives the OFDM data units 302 via respective sub-channelsof the WLAN 10 allocated for uplink transmission of the OFDM data units302 from the client stations, in an embodiment. For example, the OFDMdata unit 302-1 is transmitted via a first 20 MHZ sub-channel of theWLAN 10, the OFDM data unit 302-2 is transmitted via a second 20 MHzsub-channel of the WLAN 10, and the OFDM data unit 302-3 is transmittedvia a 40 MHz sub-channel of the WLAN 10, in the illustrated embodiment.

In an embodiment, each of the OFDM data units 302 includes a preambleincluding one or more legacy short training fields (L-STF) 304, one ormore legacy long training fields (L-LTF) 306, one or more legacy signalfields (L-SIG) 308, one or more first high efficiency WLAN signal field(HEW-SIG-A) 310, N HEW long training fields (HEW-LTF) and a second HEWsignal field (HEW-SIGB) 314. Additionally, each OFDM data unit 302includes a high efficiency WLAN data portion (HEW-DATA) 318. In anembodiment, each L-LSF field 306, each L-LTF field 308, each L-SIG field310 and each HEW-SIGA field 312 occupies a smallest bandwidth supportedby the WLAN 10 (e.g., 20 MHz). In an embodiment, if an OFDM data unit302 occupies a bandwidth that is greater than the smallest bandwidth ofthe WLAN 10, then each L-LSF field 306, each L-LTF field 308, each L-SIGfield 310 and each HEW-SIGA field 312 is duplicated in each smallestbandwidth portion of the OFDM data unit 302 (e.g., in each 20 MHzportion of the data unit 302). On the other hand, each HEW-STF field312, each HEW-LTF field 314, each HEW-SIGB field 316 and each HEW dataportion 318 occupies an entire bandwidth of the corresponding OFDM dataunit 302, in an embodiment. For example, the OFDM data unit 302-3occupies 40 MHz, wherein L-LSF field 306, the L-LTF field 308, L-SIGfield 310 and HEW-SIGA fields 312 is duplicated in the upper and thelower 20 MHz bands of the OFDM data unit 302-3, while each of theHEW-STF field 312, each of the HEW-LTF fields 314, each of the HEW-SIGBfield 316 and each of the HEW data portion 318 occupies the entire 40MHz bandwidth of the data unit 302, in the illustrated embodiment.

In an embodiment, padding is used in one or more of the OFDM data units302 to equalize lengths of the OFDM data units 302. Accordingly, thelength of each of the OFDM data units 302 correspond to the length ofthe OFDMA data unit 302, in this embodiment. Ensuring that the OFDM dataunits 302 are of equal lengths synchronizes transmission ofacknowledgment frames by client stations 25 that receive the data units302, in an embodiment. In an embodiment, each of one or more of the OFDMdata units 302 is an aggregate MAC service data units (A-MPDU) (e.g., avery high throughput (VHT) A-MPDU, an HEW MPDU, or another suitableaggregated data unit), which is in turn included in a PHY protocol dataunit (PPDU). In another embodiment, each of one or more of the OFDM dataunits 302 is a single MPDU (e.g., a VHT MPDU, an HEW MPDU, or anothersuitable non-aggregated data unit) which is in turn included in a PPDU.In an embodiment, padding (e.g., zero-padding) within one or more of theA-MPDUs 302 or single MPDUs 302 is used to equalize the lengths of thedata units 302, and to synchronize transmission of acknowledgementframes corresponding to the OFDMA data unit 300.

FIG. 4 is a diagram of an example OFDMA data unit 350, according toanother embodiment. The OFDMA data unit 350 is similar to the OFDMA dataunit 300 of FIG. 3 except that the OFDMA data unit 350 includes an OFDMAdata unit 302-4 formatted according to a legacy communication protocolthat does not support OFDMA communication (e.g., the IEEE 802.11acStandard).

In an embodiment, the AP 14 forms OFDMA groups of client stations 25,and informs the client stations 25 that the client stations 25 aremembers of particular OFDMA groups. For example, in an embodiment, theAP assigns a group number to an OFDMA group of client stations 25, andtransmits a management or a control frame that signals the group IDnumber to the client stations 25 that belong to the OFDMA group. Forexample, the management or control frame includes the group ID numberand a respective unique identifier of each of the client stations 25that belongs to the group, in an embodiment. In an embodiment, the AP 14allocates respective OFDM sub-channels to client stations 25 that belongto an OFDMA group, and provides channel allocation information to theclient stations 25 of the OFDMA group. In an embodiment, the AP 14allocates respective OFDM sub-channels to client stations 25 dynamicallywithout pre-defining an OFDMA group. The client stations 25 of the OFDMAgroup subsequently receive data in the respective OFDM sub-channelsallocated to the client stations 25 when the data is transmitted to theclient stations 25 in an OFDMA transmission from the AP 14 to the clientstations 25, in an embodiment and/or scenario. In another embodimentand/or scenario, the client stations 25 of the OFDMA group subsequentlytransmit respective data as part of an OFDMA transmission to the AP 14by transmitting the data in the respective OFDM sub-channels allocatedto the client stations 25 by the AP 14.

FIG. 5 is an example broadcast block acknowledgment field 500, accordingto an embodiment. In an embodiment, the broadcast block acknowledgmentfield 500 is included in an acknowledgment frame that the AP 14transmits to client stations 25 in response to receipt of respectiveaggregate media access control protocol data units (A-MPDUs) from theclient stations 25. The broadcast block acknowledgment field 500includes a plurality of association identifier (AID) subfields 502 and acorresponding plurality of bitmap subfields 504. In an embodiment, theAID subfields 502 include as many subfields as there are client stations25 assigned to an OFDMA group and each of the client stations has acorresponding bitmap subfield 504. In another embodiment, the AIDsubfields 502 include as many subfields as there are client stations 25that have transmitted respective A-MPDUs prior to the acknowledgmentframe. For example, as shown in FIG. 5, the AID subfields 502 include afirst AID (AID1) subfield 502-1, a second AID (AID2) subfield 502-2, anda third AID (AID3) subfield 502-3 with corresponding first bitmap (BM1)subfield 504-1, second bitmap (BM2) subfield 504-2, and third bitmap(BM3) subfield 504-3. In one embodiment, the broadcast blockacknowledgment field 500 is generated by the host processor 15 (e.g., bya management processing unit of the host processor 15). In anotherembodiment, at least one of the AID subfields 502, and/or informationincluded therein, are generated at least in part by the MAC processingunit 18. The bitmap subfield 504 includes a bitmap having as many bitsas MPDUs transmitted by the corresponding client station 25. Forexample, in an embodiment, a client station 25 transmits an A-MPDUhaving six MPDUs to the AP 14 and, in response, the AP 14 transmits anacknowledgment frame having a bitmap subfield 504 with a size of sixbits. In this embodiment, each bit of the bitmap indicates whether thecorresponding MPDU was successfully received.

FIG. 6 is diagram illustrating a frame exchange 600 between an AP (e.g.,the AP 14) and multiple client stations (e.g., multiple client stations25), according to an embodiment. During a time t1, the AP 14 transmitsan OFDMA data unit 602 directed to a plurality of client stations. In anembodiment, the AP 14 uses a medium access procedure or backoffprocedure to determine when to transmit the downlink OFDMA data unit602. In an embodiment, the backoff procedure is an enhanced distributedchannel access (EDCA) backoff procedure (e.g., shared with single userEDCA traffic). In an embodiment, the backoff procedure is a backoffprocedure specific to OFDMA. The OFDMA data unit 602 occupies an 80 MHzchannel, in the illustrated embodiment. In an embodiment, the data unit602 is the same as or similar to the data unit 300 of FIG. 3. In anembodiment, prior to transmission of the OFDMA data unit 602, the AP 14conducts a suitable channel assessment procedure, such as a carriersense multiple access with collision avoidance procedure (CSMA/CA)procedure, and based on the channel assessment procedure determines abandwidth available for transmission by the AP 14. In an embodiment, theOFDM channel includes the primary channel of the WLAN 10 and one or moresecondary channels of the WLAN 10. For example, the AP 14 determinesthat the primary 20 MHz channel and three secondary 20 MHz channels ofthe WLAN 10 are available for 80 MHz transmission by the AP 14, in theillustrated embodiment.

In an embodiment, the OFDMA data unit 602 includes a plurality of OFDMdata units 604 directed to respective client stations 25, each OFDM dataunit 604 transmitted in a respective sub-channel of the WLAN 10 to aparticular client station 25. In particular, a first OFDM data unit604-1 is directed to a first client station STA1 (e.g., the clientstation 25-1), a second OFDM data unit 604-2 is directed to a secondclient station STA2 (e.g., the client station 25-2), and a third OFDMdata unit 604-3 is directed to a third client station STA3 (e.g., theclient station 25-3), in the illustrated embodiment. In an embodiment,the first OFDM data unit 604-1 occupies the highest 20 MHz sub-channelof the 80 MHz channel, the second OFDM data unit 604-2 occupies thesecond highest 20 MHz sub-channel of the 80 MHz channel, and the thirdOFDM data unit 604-3 is transmitted in a 40 MHZ sub-channel thatincludes the lowest two 20 MHZ sub-channels of the 80 MHz channel.

In an embodiment, the preamble of the OFDMA data unit 600 is transmittedin each of the 20 MHz sub-channels occupied by the OFDMA data unit 602.In an embodiment, the preamble of the OFDMA data unit 600 includes achannel allocation field (e.g., in a signal field of the preamble suchas the HEW-SIGA field of the preamble) that indicates to the clientstations 25 to which the OFDMA data unit 600 is directed that the clientstation 25 are intended recipients of different portions of the OFDMAdata unit 600. An example of a channel allocation field is described inU.S. patent application Ser. No. 14/538,573, entitled “Medium AccessControl for Multi-Channel OFDM in a Wireless Local Area Network,” filedon Nov. 11, 2014, the disclosure of which is hereby incorporated hereinby reference in its entirety.

Each of the client stations 25 receives the channel allocation field inthe primary channel of the WLAN 10 (e.g., in the lowest 20 MHz channel)and determines, based on the channel allocation field, which channel ofthe WLAN 10 includes data directed to the client station 25,respectively, in an embodiment. The client stations 25 tune to theappropriate sub-channels indicated in the channel allocation field andreceive data directed to the client stations 25 via the respectivesub-channels allocated to the client station 25. During a time t2, in anembodiment, client stations 25 that successfully receive data in therespective sub-channels allocated to the client stations 25 transmitrespective acknowledgement (ACK or BlkAck) frames 606 to the AP 14. Inan embodiment, each client station 25 transmits its acknowledgement (ACKor BlkAck) frame 606 in the respective sub-channel allocated to theclient station 25. In an embodiment, the AP 14 allocates a sub-channelfor the acknowledgment to be transmitted from each client station thatis different from a sub-channel allocated for downlink OFDMAtransmissions to the corresponding client station. In an embodiment, theAP 14 synchronizes transmission of the ACK frames 606 from the clientstations 25 by ensuring that the OFDM data units 604-1, 604-2, 604-3 areof equal length. For example, the AP adds padding bits (e.g., bitshaving predetermined values such as zero bits or one bits) to data bitsin one or more of the data units 604 to equalize lengths of the dataunits 604, in an embodiment. For example, in an embodiment in which theOFDM data units 604-1, 604-2, 604-3 are A-MPDUs, and the AP 14 utilizesA-MPDU padding in one or more of the data units 604-1, 604-2, 604-3 toensure that the data units 604-1, 604-2, 604-3 are of the same length.As another example, in an embodiment in which the OFDM data units 604-1,604-2, 604-3 are MPDUs, and the AP 14 utilizes MPDU padding in one ormore of the data units 604-1, 604-2, 604-3 to ensure that the data units604-1, 604-2, 604-3 are of the same length.

In another embodiment, the ACK frames 606 are not simultaneouslytransmitted by the client stations 25. For example, transmission of theACK frames 506 is staggered among the client stations 25, in anembodiment. For example, the AP provides to the client stations 25indications of different specific times at which to transmit theirrespective ACK frames 606, or a specific order in which to transmittheir respective ACK frames 606, and the client stations 25 transmit theACK frames 606 at the specific times or in the specific order indicatedby the AP, in an embodiment.

In an embodiment, the ACK frames 606 are block acknowledgement (BlkAck)frames that indicate successful or unsuccessful reception of a pluralityof data units, such as of a plurality of data units aggregated in thecorresponding A-MPDU 602. Generally speaking, as used herein, the terms“acknowledgement frame” and “ACK frame” are used interchangeably andencompass both an acknowledgement frame that acknowledges successful orunsuccessful receipt of a single data unit, and a block acknowledgementframe that acknowledges successful or unsuccessful receipt of multipledata units (e.g., multiple data units transmitted as parts of anaggregated data unit).

In an embodiment, the bandwidth of acknowledgment 606 is not wider thanthe bandwidth of downlink OFDMA transmission 602, and in each 20 MHzchannel occupied by the downlink OFDMA transmission 602, there is atleast one sub-channel for transmission of the acknowledgment.

In some embodiments, the AP 14 transmits a control frame, such as ascheduling frame, to the client stations 25 prior to transmission of anOFDMA data unit to the client stations 25. In an embodiment, the controlframe that the AP 14 transmits to the client stations 25 prior totransmission of an OFDMA data unit to the client stations 25 is a legacy(e.g., an IEEE 802.11 a or an IEEE 802.11 g) duplicate control framethat is replicated in each smallest bandwidth band (e.g., each 20 MHzband) of the WLAN 10. In an embodiment, the AP 14 transmits the controlframe at the beginning of a transmission opportunity (TXOP) to informthe client stations 25 whether the client stations 25 are to receivedata from the AP 14 and/or are to transmit data to the AP 14 during theTXOP. The control frame includes downlink and/or uplink channelallocation information that indicates to the client stations 25 that areto receive and/or transmit data which sub-channels to use for receptionand/or transmission of data, in an embodiment. In an embodiment, thedownlink channel allocation information is carried in a downlink PHYsignal field (e.g., a SIG field). In one such embodiment, a separatecontrol frame is omitted. In an embodiment, the client stations 25 areconfigured to determine their respective downlink sub-channels based ondownlink channel allocation information included in the control frameand to subsequently simultaneously receive, via the downlinksub-channels, data from the AP 14 with the other client stations 25 aspart of a downlink OFDMA transmission from the AP 14. Similarly, theclient stations 25 are configured to determine their respective uplinkchannels based on uplink channel allocation information included in thecontrol frame and to subsequently simultaneously transmit data to the AP14 with the other client stations 25 as part of an uplink OFDMAtransmission to the AP 14, in an embodiment.

In at least some embodiments in which the AP 14 transmits a controlframe to the client stations 25 to signal downlink channel allocation tothe client stations 25 for a downlink OFDMA transmission to the clientstations 25, such channel allocation information need not be included ina preamble of each of the OFDM data unit transmitted as part of theOFDMA transmission. In one such embodiment, the preamble of each dataunit in an OFDMA transmission is generally the same as a preamble usedfor regular OFDM transmission to single client station 25. For example,with reference to FIGS. 3 and 4, the signal field 310 of each of thedata units 302 is the same as a HEW-SIGA field of a data unittransmitted as a regular transmission to a single client station 25. Inanother embodiment, the preamble of each OFDM data unit included in theOFDMA transition is substantially the same as a preamble used forregular OFDM transmission to single client station 25, but includes anindication that the OFDM data unit is part of an OFDMA transmission tomultiple client stations 25. For example, with reference to FIGS. 3 and4, one or more bits of the signal field 310 is/are set to indicate thatthe OFDM data units 302 are part of an OFDMA transmission, in anembodiment.

FIG. 7 is a diagram illustrating various acknowledgment types duringsingle user frame exchanges 700, 710, and 720 for a transmissionopportunity (TXOP) holder using enhanced distributed channel access(EDCA), according to an embodiment. The frame exchanges 700, 710, and720 are “single user” in that each includes a transmission of an A-MPDUfrom a single access point (e.g., the AP 14) to a single client station(e.g., client station 25-1). In an embodiment, an AP 14 obtains a TXOPand transmits one or more A-MPDUs to a client station 25. In theembodiment shown in FIG. 7, each frame exchange 700, 710, and 720 isperformed within a TXOP of the AP 14. In an embodiment, the TXOP holder(e.g., the AP 14) indicates the acknowledgment type (e.g., NormalAcknowledgment, Implicit Block Acknowledgment, No Acknowledgment, NoExplicit Acknowledgment, Block Acknowledgment) through an AcknowledgmentPolicy in a header of at least some of its transmitted frames, forexample, in a Quality of Service (QoS) control field.

The frame exchange 700 illustrates a Block Acknowledgment where theclient station 25 does not provide an immediate acknowledgment to framesreceived from the AP 14. In the embodiment shown in FIG. 7, during theframe exchange 700, the AP 14 transmits a first A-MPDU 702 and a secondA-MPDU 704 in a downlink (DL) direction to the client station 25 (STA1).In an embodiment, the client station 25 waits for receipt of a blockacknowledgment request (BAR) 706 from the AP 14 before sending a blockacknowledgment 708 to the AP 14. The frame exchange 710 illustrates anImplicit Block Acknowledgment where the client station 25 transmits ablock acknowledgment 714 in response to and upon receipt of an A-MPDU712. The frame exchange 720 illustrates a Normal Acknowledgment wherethe client station 25 transmits an acknowledgment 724 in response to andupon receipt of a very high throughput (VHT) single MPDU or MPDU 722.

In some embodiments and/or scenarios, the AP 14 selects one or morequality of service indicators (e.g., traffic classes or accesscategories) for a frame exchange. In some embodiments, the AP 14 selectsthe quality of service indicator based on a medium access procedure usedto trigger the frame exchange. In an embodiment, the blockacknowledgment allows the AP 14 to select frames having differenttraffic classes (TC) and/or frames intended for different receiveraddresses (RA) for inclusion within a same A-MPDU. In an embodiment, theAP 14 selects data frames with a same access category (AC) to beencapsulated within an A-MPDU. In an embodiment, responding frames(e.g., the acknowledgments 708, 714, and 724) have a same bandwidth as apreceding frame which elicits the responding frame (e.g., the blockacknowledgment request 706, the A-MPDU 712, or the A-MPDU 722), with theexception of clear to send (CTS) frames which may have a smallerbandwidth than a preceding request to send (RTS) frame. Whentransmitting a frame, the TXOP holder uses a bandwidth that is not widerthan i) a preceding frame or ii) the elicited acknowledgment when aduplicate frame was not previously transmitted. Otherwise, the TXOPholder uses a bandwidth that is not wider than a preceding duplicate CTSframe.

FIG. 8 is a diagram illustrating a block acknowledgment during a frameexchange 800 for a TXOP holder using EDCA, according to an embodiment.In an embodiment, the frame exchange 800 is a “multi-user” in that anaccess point (e.g., the AP 14) performs a multi-user multiple input,multiple output (MU-MIMO) transmission 804 having separate OFDM dataunits 806-1 and 806-2 intended for two client stations STA1 and STA2(e.g., client stations 25-1 and 25-2). In an embodiment, the AP 14obtains a TXOP and simultaneously transmits a first A-MPDU 806-1 to theclient station 25-1 and transmits a second A-MPDU 806-2 to the clientstation 25-2 using different sub-channels (i.e., space time streams) ofa MU-MIMO communication channel. In the embodiment shown in FIG. 8, theMU-MIMO transmission 804 includes data frames from a same accesscategory (AC). In the simultaneously transmitted A-MPDUs 806-1 and806-2, data frames from a same AC are encapsulated in each A-MPDU by theAP 14, in an embodiment. In some embodiments, when TXOP sharing isallowed, data frames from different ACs are encapsulated in differentA-MPDUs within the TXOP. In one such embodiment, the MPDUs from aprimary AC have higher priority to be transmitted. When TXOP sharing isnot allowed, data frames from the primary AC can be encapsulated indifferent A-MPDUs.

In the embodiment shown in FIG. 8, the A-MPDU 806-1 corresponds to anindication of an Implicit Block Acknowledgment and the A-MPDU 806-2corresponds to an indication of a Block Acknowledgment. Based on theindication of the Implicit Block Acknowledgment, the client station 25-1transmits a block acknowledgment 810 to the AP 14 in response to andupon receipt of the A-MPDU 806-1. The client station 25-2, based on theindication of the Block Acknowledgment, waits for receipt of a blockacknowledgment request (BAR) 820 from the AP 14 before sending a blockacknowledgment 830 to the AP 14. The block acknowledgment 830, in someembodiments, is transmitted using a same bandwidth as the originalMU-MIMO transmission 804. For example, in an embodiment, the MU-MIMOtransmission 804 occupies a bandwidth of 40 MHz (e.g., 2×20 MHzsub-channels) and the block acknowledgment 830 is duplicated across asame bandwidth.

FIG. 9 is a diagram illustrating a frame exchange 900 between an AP(e.g., AP 14) and a plurality of client stations (e.g., client stations25) that includes an uplink transmission of data from the plurality ofclient stations to the AP, according to an embodiment. In someembodiments, the uplink transmission includes a MU-MIMO datatransmission. In some embodiments, the uplink transmission includes anOFDMA data transmission.

During a time t1, the AP 14 transmits an uplink scheduling frame 904 toa plurality of client stations 25. In an embodiment, the time t1 beginsat the beginning of a TXOP 902 obtained by (e.g., based on a suitablechannel assessment procedure, such as CSMA/CA), or scheduled for (e.g.,through a target wake time (TWT) service period), the AP 14. In anembodiment, the uplink scheduling frame 904 provides, to the pluralityof client stations 25, MU-MIMO uplink scheduling information to be usedfor transmission of an uplink OFDM data unit during the TXOP 902 via anallocated space time stream. In an embodiment, the uplink schedulingframe 904 includes MU-MIMO scheduling information, for example, one ormore identifiers of space time streams for the client stations. In anembodiment, the scheduling frame 904 further indicates, to each of theclient stations STA1 and STA2 a length or duration to be used fortransmission of an uplink data unit during the TXOP 902. In anotherembodiment, the uplink scheduling frame 904 provides, to the pluralityof client stations 25, OFDMA uplink scheduling information to be usedfor transmission of an uplink OFDM data unit during the TXOP 902 via asub-channel of the OFDM communication channel. In an embodiment, theuplink scheduling frame 904 includes OFDMA scheduling information, forexample, one or more identifiers of transmission bandwidth for theclient stations. In an embodiment, the scheduling frame 904 furtherindicates, to each of the client stations STA1 and STA2 a length orduration to be used for transmission of an uplink data unit during theTXOP 902.

In an embodiment, the scheduling frame 904 is a synchronization (SYNC)frame, control frame, trigger frame, or other suitable frame. In anembodiment, the scheduling frame 904 is a non-data packet (NDP) framethat omits a payload. In one embodiment in which the scheduling frame904 in an NDP frame, MAC layer information, e.g., receiver address,transmitter address, etc., is included in a signal field of a PHYpreamble of the scheduling frame 904. In an embodiment and/or scenario,the uplink scheduling frame 904 is duplicated in each smallest bandwidthportion (e.g., in each 20 MHz) of the entire bandwidth of the TXOP 902.In another embodiment and/or scenario, the scheduling frame 904 occupiesthe entire bandwidth of the TXOP 902, for example when each of theclient stations 25 to which the scheduling frame 904 is transmitted iscapable of operating in the entire bandwidth of the TXOP 902. In anotherembodiment and/or scenario, the uplink scheduling frame 904 isduplicated in every bandwidth portion of the entire bandwidth of theTXOP 902 so as to allow each client station 25 to which the schedulingframe 904 is transmitted to receive and decode the scheduling frame 904,according to capabilities of the client stations 25 to which thescheduling frame 904 is directed. For example, if the entire bandwidthof the TXOP is 160 MHz, but at least one of the client stations 25 towhich the scheduling frame 904 is directed is capable to operate with amaximum bandwidth of 80 MHz, then the scheduling frame 904 occupies 80MHz and is duplicated in each 80 MHz portion of the entire bandwidth ofthe TXOP (i.e., in the lower 80 MHz portion and the upper 80 MHzportion), in an embodiment.

The scheduling frame 904 indicates different sub-channels allocated foruplink transmission by the client stations, in various embodiments.While only two client stations STA1 and STA2 are shown in FIG. 9, thescheduling frame 904 indicates sub-channels allocated for three, four,or another suitable number of client stations in other embodimentsand/or scenarios. In an embodiment, the scheduling frame 904 indicates afirst space time stream allocated to STA1 and a second space time streamallocated to STA2 for a MU-MIMO transmission. In another embodiment, thescheduling frame 904 indicates a first 20 MHz bandwidth of a 40 MHz OFDMcommunication channel allocated to STA1 and a second 20 MHz bandwidth ofthe 40 MHz OFDM communication channel allocated to STA2 for an OFDMAtransmission. In other embodiments, the AP 14 allocates other suitablecombinations of sub-channels to the client stations. In an embodiment,the AP 14 allocates an equal number of sub-channels to each clientstation. In another embodiment, the AP 14 allocates an unequal number ofsub-channels to the client stations. In one such embodiment, the AP 14allocates a 20 MHz sub-channel to a first client station and a 60 MHzsub-channel (e.g., three separate 20 MHz sub-channels) to a secondclient station.

During a time t2, the plurality of client stations 25 transmitrespective OFDM data units 908 to the AP 14. Time t2 at each clientstation 25 begins upon expiration of a predetermined time interval, suchas for example a time interval corresponding to a short inter-framespace (SIFS), after completion of reception, of the scheduling frame 904at the client station 25, in an embodiment. In another embodiment, apredetermined time period that is greater than SIFS is defined, and timet2 at each client station 25 begins upon expiration of a predeterminedtime interval corresponding to the predetermined time interval greaterthan SIFS. For example, a predetermined time period that is greater thanSIFS and less than point coordination function (PCF) interframe space(PIFS) is defined. The greater predetermined time interval may providesufficient time for the client stations 25 to decode the schedulingframe 904 and to prepare for uplink transmission based on the uplinkscheduling information provided by the scheduling frame 904, in at leastsome embodiments. Additionally or alternatively, the scheduling frame904 includes one or more padding bits at the end of the scheduling frame904 to provide sufficient time for the client stations 25 to prepare foruplink transmission based on the uplink scheduling information providedby the scheduling frame 904, in some embodiments. For example, a MACheader included in the scheduling frame 904 indicates a length of avalid payload, wherein the one or more padding bits follow the validpayload, in an embodiment. Further, a signal field of a PHY preamble ofthe scheduling frame 904 includes an indication of the entire length ofthe scheduling frame 904, which includes the one or more padding bits atthe end of the scheduling frame 904, in an embodiment.

In an embodiment, each client station 25 transmits its OFDM data unit908 during the time t2 in a respective sub-channel, allocated to theclient station 25, as indicated in the scheduling frame 904. In anembodiment, the length or duration of each of the OFDM data units 908corresponds to the length or duration indicated in the scheduling frame904.

During a time t3, the AP 14 transmits respective ACK frames 910 and 912to the client stations 25 (STA1 and STA2) acknowledging receipt of theOFDM data units 908 from the client stations 25. Time t3 begins uponexpiration of a predetermined time interval, such as for example a timeinterval corresponding to a short inter-frame space (SIFS), aftercompletion of reception of the OFDM data units 908 at the AP 14, in anembodiment. In an embodiment, the AP 14 transmits the ACK frames 910 and912 to the client stations 25, as parts of a MU-MIMO transmission to theclient stations 25, in the respective sub-channels allocated to theclient stations 25 indicated in the scheduling frame 904 (e.g., in asame bandwidth as the corresponding scheduling frame). In anotherembodiment, the AP 14 transmits the ACK frames 910 and 912 to the clientstations 25 as parts of an OFDMA transmission to the client stations 25in the respective sub-channels allocated to the client stations 25indicated in the scheduling frame 904. In some embodiments, anacknowledgment policy indicates whether an acknowledgment to an uplinkOFDM data unit is required or optional and whether the acknowledgmentshould be sent in response to the receipt of the OFDM data unit ordelayed. In an embodiment, the AP 14 determines an order in whichacknowledgments are to be transmitted in response to receipt of theuplink OFDM data units from the client stations. In some embodiments,the ACK frames 910 and 912 are duplicated in each smallest bandwidthportion (e.g., in each 20 MHz) of the entire bandwidth of the TXOP 902.For example, in an embodiment, the AP transmits a legacy OFDM data unitas the ACK frames 910 and 912.

In an embodiment, the AP 14 is configured to transmit a broadcastacknowledgement frame 960 instead of the ACK frames 910 and 912. FIG. 9illustrates a TXOP 952 of the AP 14, during which the AP transmits ascheduling frame 954 and receives uplink OFDM data units 958 from theclient stations 25. The TXOP 952 is generally similar to the TXOP 902,except that the AP 14 transmits a broadcast acknowledgement frame 960that includes respective acknowledgements for the client stations 25 andomits the ACK frames 910 and 912. In an embodiment, the broadcastacknowledgment frame 960 includes the broadcast block acknowledgmentfield 500, as described above with respect to FIG. 5. In someembodiments, the AP 14 performs more than one frame exchange during aTXOP. In the embodiment shown in FIG. 9, the TXOP 952 includes a firstframe exchange (i.e., scheduling frame 954, uplink OFDM data units 958,and broadcast acknowledgment frame 960) and a second frame exchange. Thesecond frame exchange includes a scheduling frame 964, an uplink OFDMdata unit 968, and a block acknowledgment frame 970.

In some embodiments, the client station 25 is configured to respond to ascheduling frame without determining whether the sub-channel indicatedin the scheduling frame is busy during a time period between the receiptof the scheduling frame and the transmission of the uplink OFDM dataunit. In other embodiments, the client station 25 is configured todetermine whether the allocated sub-channel is busy. In an embodiment,the client station is allocated one sub-channel and in response to adetermination that the one sub-channel is busy, the client station omitstransmitting the uplink OFDM data unit. In an embodiment, when at leastone 20 MHz channel that covers the client station's sub-channel is busy,the sub-channel of the client station is determined to be busy. In otherembodiments, the client station is allocated a primary 20 MHz channeland at least one additional sub-channel is allocated to the STA. Inanother embodiment, when at least a portion of the client station'ssub-channel is determined to be busy (e.g., a 20 MHz bandwidth portionis busy within a 40 MHz sub-channel), the client station omitstransmitting uplink OFDM data units on only those sub-channels which aredetermined to be busy. In some embodiments, the client station 25determines whether a primary channel or sub-channel of a communicationchannel is busy using a network access allocation (NAV) timer. In someembodiments, the client station 25 determines whether a non-primarychannel is busy based on an idle period corresponding to a pointcoordination function (PCF) interframe space (PIFS) between the receiptof the scheduling frame and the transmission of the uplink OFDM dataunit. Other interframe spaces can also be used for an idle/busydetermination. In an embodiment, a client station makes an idle/busydetermination in an entire bandwidth of a trigger frame (e.g., thesynchronization frame 904). If the determination result is busy, theclient station will not transmit the uplink OFDMA frames.

In an embodiment, the uplink OFDM data unit 908 acts as anacknowledgment of the scheduling frame 904. In one such embodiment, theAP 14 determines whether the scheduling frame 904 was transmittedcorrectly based upon whether an uplink OFDM data unit is received aftertransmission of the scheduling frame 904. In an embodiment, for example,when the AP 14 receives the uplink OFDM data unit from at least oneclient station that responds to a first scheduling frame of a TXOP, theAP continues to use the TXOP for frame exchanges. In another embodiment,when the AP does not receive an uplink OFDM data unit in response to thescheduling frame, the AP does not send downlink OFDM data units for theremainder of the TXOP to those client stations that did not respond.

In an embodiment, the total bandwidth of the uplink OFDMA transmissionis determined based on the bandwidth of the trigger frame. In one suchembodiment, the sub-channel of a client station does not include a 20MHz channel that is not covered by the bandwidth of the trigger frame.In an embodiment, in each 20 MHz channel that is covered by thetransmission of the trigger frame, there is at least one sub-channelallocated to a client station.

FIG. 10 is a frame exchange between an AP 14 and a plurality of clientstations 25 that includes uplink OFDMA transmission of data from theplurality client stations 25 to the AP 14, according to anotherembodiment. In some embodiments, the AP uses the backoff procedure todetermine when to transmit the uplink scheduling frame 1002. In anembodiment, the backoff procedure use the EDCA backoff procedure (sharedwith single user EDCA traffic). In an embodiment, the backoff procedureis a backoff procedure specific to OFDMA. During a time t1, the AP 14transmits an uplink scheduling frame 1002 to a plurality of clientstations 25. In an embodiment, the uplink scheduling frame 1002 isgenerally similar to the uplink scheduling frame 904. In an embodiment,the time t1 begins at the beginning of a TXOP obtained by (e.g., basedon a suitable channel assessment procedure, such as CSMA/CA), orscheduled for (e.g. through a target wake time (TWT) service period),the AP 14. In an embodiment, the uplink scheduling frame 1002 provides,to the plurality of client stations 25, OFDMA uplink schedulinginformation to be used for transmission of an uplink OFDMA data unitduring the TXOP. In an embodiment, the scheduling frame 1002 furtherindicates, to each of the client stations STA1, STA2, STA3, a length orduration to be used for transmission of an uplink data unit during theTXOP.

In an embodiment and/or scenario, the uplink scheduling frame 1002 isduplicated in each smallest bandwidth portion (e.g., in each 20 MHz) ofthe entire bandwidth of the TXOP. In another embodiment and/or scenario,the scheduling frame 1002 occupies the entire bandwidth of the TXOP, forexample when each of the client stations 25 to which the schedulingframe 1002 is transmitted is capable of operating in the entirebandwidth of the TXOP. In another embodiment and/or scenario, the uplinkscheduling frame 1002 is duplicated in every bandwidth portion of theentire bandwidth of the TXOP so as to allow each client station 25 towhich the scheduling frame 1002 is transmitted to receive and decode thescheduling frame 1002, according to capabilities of the client stations25 to which the scheduling frame 1002 is directed.

The scheduling frame 1002 indicates respective sub-channels allocatedfor uplink OFDMA transmission by three client stations STA1, STA2 andSTA3, in the illustrated embodiment. For example, the scheduling frame1002 indicates channel allocation within an 80 MHz channel, andindicates that (i) the highest 20 MHz sub-channel of the 80 MHz channelis allocated to STA2, (ii) the second highest 20 MHz sub-channel of the80 MHz channel is allocated to STA1 and (iii) a 40 MHz sub-channel thatincludes the second lowest 20 MHz sub-channel and the lowest 20 MHzsub-channel is allocated to STA0, in an embodiment.

During a time t2, the plurality of client stations 25 transmitrespective OFDM data units 1006 that collectively form an OFDMA dataunit 1004 to the AP 14. The OFDM data units 1006 are generally similarto uplink OFDM data unit 908, except that the client station STA1 doesnot respond to the scheduling frame 1002, for example, because theclient station STA1 does not receive the trigger frame correctly ordetects a busy medium in its allocated sub-channel. In an embodiment,each client station 25 transmits its OFDM data unit 1006 during the timet2 in a respective sub-channel, allocated to the client station 25, asindicated in the scheduling frame 1002. In an embodiment, the length orduration of each of the OFDM data units 1006 corresponds to the lengthor duration indicated in the scheduling frame 1002.

During a time t3, the AP 14 transmits respective ACK frames 1008 to theclient stations 25 (STA0, STA2) acknowledging receipt of the OFDM dataunits 1006 from the client stations 25. The ACK frames 1008 aregenerally similar to the ACK frames 910 and 912, in an embodiment. Inanother embodiment, the AP 14 transmits a broadcast acknowledgementframe that includes respective acknowledgements for the client stations25 (STA0, STA2). In an embodiment, the AP 14 transmits the ACK frames1008 to the client stations 25, as parts of an OFDMA transmission to theclient stations 25, in the respective sub-channels allocated to theclient stations 25 indicated in the scheduling frame 1002. In anembodiment, a negative acknowledgment (NAK) is transmitted to STA1because the AP did not receive uplink frames from STA1 in t2. In anembodiment, the NAK is a Quality of Service (QoS) Null frame or an MPDUDelimiter. In an embodiment, without bandwidth protection provided by arequest to send/clear to send (RTS/CTS) exchange, the scheduling framedetermines a bandwidth of a frame exchange and subsequent frameexchanges within a TXOP. In the illustrated embodiment, the AP 14transmits the ACK frames 1008 to each of the plurality of clientstations, including the NAK to the client station STA1, in order tomaintain the entire bandwidth (e.g., 80 MHz, including the 20 MHzallocated to STA1) of the communication channel. In the illustratedembodiment, the client station STA1 transmits an uplink OFDM data unitwithout determining whether the sub-channel indicated in the schedulingframe 1012 is busy.

In the illustrated embodiment of FIG. 10, the AP 14 transmits anadditional scheduling frame 1012 during a same TXOP as the 1002. Thescheduling frame 1012 indicates respective sub-channels allocated foruplink OFDMA transmission by the three client stations STA0, STA1 andSTA2, in an embodiment. For example, the AP 14 makes additional attemptsto use the second highest 20 MHz sub-channel to determine whether thesub-channel is no longer busy.

FIG. 11 is a frame exchange 1100 between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.The frame exchange 1100 is generally similar to the frame exchange 1000,except that a scheduling frame 1112 is transmitted within a same TXOPafter a scheduling frame 1102 allocates a total bandwidth that is lessthan the scheduling frame 1102. In the embodiment shown, the highest andthe second highest 20 MHz sub-channels of the 80 MHz channel are notallocated by the scheduling frame 1112.

FIG. 12 is a frame exchange 1200 between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.The frame exchange 1200 is generally similar to the frame exchange 1000,except that the sub-channel allocated to the client station STA1 is notused for the client station STA1 in the following OFDMA transmissionwhen the AP 14 does not receive frames in the first uplink frameexchange from the client station STA1 in its cub-channel. In theillustrated embodiment, the second highest 20 MHz sub-channel allocatedto the client station STA1 is not used during the TXOP. In anotherembodiment, the unused sub-channel is allocated to another clientstation for a remainder of the TXOP.

FIG. 13 is a frame exchange 1300 between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment. The frameexchange 1300 is generally similar to the frame exchange 1200, exceptthat when the AP 14 does not receive an uplink OFDM data unit on asub-channel 1305 allocated to a client station, the AP 14 does not usethe allocated sub-channel for a remainder of the TXOP.

FIG. 14 is a frame exchange 1400 between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment. The frameexchange 1400 is generally similar to the frame exchange 1000 of FIG.10, except that in the frame exchange 1400, a scheduling frame 1402indicates noncontiguous channel allocation to a plurality of clientstations 25. In an embodiment, prior to transmitting the schedulingframe 1402, the AP 14 detects that a particular sub-channel 1401 iscurrently not available (e.g., busy). For example, the AP 14 detectsthat the second highest 20 MHz sub-channel of the 80 MHz channel isbusy, while the remaining 20 MHz sub-channels of the 80 MHz areavailable. Then, during a time t1, the AP 14 transmits the schedulingframe 1402 on each of the available sub-channels of the 80 MHz channel.The scheduling frame 1402 is similar to the scheduling frame 902 exceptthat the scheduling frame 1402 indicates channels allocated to STA0 andSTA2, but not STA1, in the illustrated embodiment. In particular, thescheduling frame 1402 indicates that (i) the highest 20 MHz sub-channelof the 80 MHz channel is allocated to STA2, and (ii) a 40 MHzsub-channel that includes the second lowest 20 MHz sub-channel and thelowest 20 MHz sub-channel is allocated to STA0, in the illustratedembodiment.

In an embodiment, during a time t2, stations STA0 and STA2 transmitrespective OFDM data units 1404 that collectively form an OFDMA dataunit to the AP 14. In an embodiment, the client stations STA0 and STA2transmit their respective OFDM data units 1404 in a respectivenon-contiguous sub-channels allocated to the client stations STA0 andSTA2, as indicated in the scheduling frame 1402. During a time t3, theAP 14 transmits respective ACK frames 1408 to the client stations SATOand STA2 acknowledging successful receipt of the OFDM data units 1404from the client stations STA0 and STA2, in an embodiment. The APtransmits the ACK frame 1408 to the client stations STA0 and STA2, asparts of an OFDMA transmission to the client stations STA0 and STA2, inthe respective non-contiguous sub-channels allocated to the clientstations STA0 and STA2, in an embodiment. In another embodiment, the AP14 transmits a broadcast acknowledgement frame that includes respectiveacknowledgements for the client stations 25 (STA0 and STA2).

While an 80 MHz communication channel is allocated to the clientstations in the illustrated embodiment, the AP 14 selects othersub-channel allocations (e.g., 60 MHz, 100 MHz, 120 MHz, 140 MHz, etc.)in other embodiments and/or scenarios. In an embodiment, the AP 14selects contiguous blocks of 40 MHz, 80 MHz, or 160 MHz for an uplinkMU-MIMO transmission. In some embodiments, a physical layer clearchannel assessment (PHY-CCA) provides an idle/busy indication for each20 MHz sub-channel of a communication channel. In an embodiment, thePHY-CCA is redefined to provide at least some sub-channel allocations.

FIG. 15 is a frame exchange 1500 between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment. The frameexchange 1500 is generally similar to the frame exchange 1000 of FIG.10, except that in the frame exchange 1500, the total bandwidth of theOFDMA transmission is not one of 20/40/80/160/80+80 MHz. In anembodiment, prior to transmitting the scheduling frame 1502, the AP 14detects that a particular sub-channel 1501 is currently not available(e.g., busy). For example, the AP 14 detects that the highest 20 MHzsub-channel of the 80 MHz channel is busy, while the remaining 20 MHzsub-channels of the 80 MHz are available. Then, during a time t1, the AP14 transmits the scheduling frame 1502 on each of the availablesub-channels of the 80 MHz channel. The scheduling frame 1502 is similarto the scheduling frame 902 except that the scheduling frame 1502indicates channels allocated to STA0 and STA1, but not STA2, in theillustrated embodiment. In particular, the scheduling frame 1502indicates that (i) the second highest 20 MHz sub-channel of the 80 MHzchannel is allocated to STA1, and (ii) a 40 MHz sub-channel thatincludes the second lowest 20 MHz sub-channel and the lowest 20 MHzsub-channel is allocated to STA0, in the illustrated embodiment.

FIG. 16 is a frame exchange 1600 between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to another embodiment. Inthe frame exchange 1600, the AP 14 determines that a primary sub-channel1601 of an OFDM communication channel is busy. In an embodiment, theframe exchange 1600 occurs during a scheduled service period. In thisembodiment, the AP 14 determines an availability of the sub-channel 1601of the OFDM communication channel based on an idle state during a pointcoordination function interframe space (PIFS). In an embodiment, the AP14 performs the frame exchange 1600 using only the sub-channelsdetermined to be not busy.

FIG. 17 is a frame exchange 1700 between an AP 14 and a plurality ofclient stations (STA1 and STA2) that includes downlink OFDMAtransmission 1704 of data from the AP to the plurality client stations,according to an embodiment. In an embodiment, the AP 14 obtains a TXOP1702 and simultaneously transmits a first downlink A-MPDU 1703-1 to theclient station STA1 and transmits a second downlink A-MPDU 1703-2 to theclient station STA2 using different sub-channels (i.e., tone blocks) ofan OFDMA communication channel. In some embodiments, an acknowledgmentpolicy indicates whether an acknowledgment to an uplink OFDM data unitis required or optional and whether the acknowledgment should be sent inresponse to the receipt of the OFDM data unit or delayed. In anembodiment, the AP 14 determines an order in which acknowledgments areto be transmitted in response to receipt of the uplink OFDM data unitsfrom the client stations. In the embodiment shown in FIG. 17, the firstdownlink A-MPDU 1703-1 corresponds to an indication of an Implicit BlockAcknowledgment and the second downlink A-MPDU 1703-2 corresponds to anindication of a Block Acknowledgment.

Based on the indication of the Implicit Block Acknowledgment, the clientstation STA1 transmits a block acknowledgment 1708 to the AP 14 inresponse to and upon receipt of the second downlink A-MPDU 1703-2. In anembodiment, the client station STA1 automatically transmits the blockacknowledgment 1708 after a short interframe space (SIFS) period fromthe receipt of the second downlink A-MPDU 1703-2. The client stationSTA2, based on the indication of the Block Acknowledgment, waits forreceipt of a block acknowledgment request (BAR) 1710 from the AP 14before sending a block acknowledgment 1712 to the AP 14, in anembodiment. The BAR 1710, in some embodiments, is transmitted using asame bandwidth as the original OFDMA transmission 1704. For example, inan embodiment, the OFDMA transmission 1704 occupies a bandwidth of 40MHz (e.g., 2×20 MHz sub-channels) and the BAR 1710 is duplicated acrossa same bandwidth. In various embodiments, the client stations STA1 andSTA2 transmit the block acknowledgments 1708 and 1712 to occupy a samesub-channel allocated for the corresponding A-MPDU. In an embodiment,the client station transmits the block acknowledgment using atransmission bandwidth equal to the smaller of i) the OFDMA aggregatedbandwidth and ii) a smallest bandwidth that the client station iscapable of transmitting. In another embodiment, the client stationtransmits the block acknowledgment using a transmission bandwidth equalto n*20 MHz, where n is a smallest integer value such that the blockacknowledgment occupies the same bandwidth as the downlink A-MPDU.

In some embodiments, the BAR 1710 and acknowledgment frames 1708 and1712 are duplicated in each smallest bandwidth portion (e.g., in each 20MHz) of the entire bandwidth of the TXOP 1702. For example, in anembodiment, the AP transmits a legacy OFDM data unit as the BAR 1710 andthe client stations transmit legacy OFDM data units as theacknowledgment frames 1708 and 1712. In some embodiments, the AP 14allocates different sub-channels to different client stations within asame TXOP.

FIG. 18 is a frame exchange 1800 between an AP 14 and a plurality ofclient stations STA0, STA1, STA2 that includes downlink OFDMAtransmission of data from the AP to the plurality client stations,according to an embodiment. The frame exchange 1800 includes frameexchanges 1801, 1811, and 1821 that occur during a TXOP of the AP 14.During the frame exchange 1801, the AP 14 transmits a downlink OFDMAdata unit 1802 (e.g., including A-MPDUs) to the plurality of clientstations STA2, STA1, and STA0. In an embodiment, the downlink OFDMA dataunit 1802 is generally similar to the OFDMA data unit 602. In theembodiment illustrated in FIG. 18, the AP 14 receives a blockacknowledge 1804 (e.g., an uplink OFDMA data unit) that does not includea block acknowledge from the client station STA1 on a sub-channel 1805.In some embodiments, the AP 14 allocates sub-channels based on theresponse (e.g., block acknowledgments) to a previously transmitteddownlink OFDM data unit. In an embodiment, the AP 14 determines that thesub-channel 1805 is busy or unavailable to the client station STA1 basedon the omitted block acknowledgment. In an embodiment, when the AP doesnot receive an uplink OFDM data unit in response to the downlink OFDMAdata unit, the AP does not send downlink OFDM data units for theremainder of the TXOP to those client stations that did not respond.

In an embodiment, the AP 14 transmits a downlink OFDMA data unit havinga non-contiguous sub-channel allocation. In an embodiment, for example,based on the determination that an acknowledgment to the previous OFDMdata unit was not received, the AP 14 transmits a downlink OFDMA dataunit 1812 that omits an OFDM data unit on the sub-channel 1805 duringthe frame exchange 1811. In an embodiment, the AP 14 allocates thesub-channel 1805 to another client station during the frame exchange1821. In the embodiment shown in FIG. 18, the AP 14 allocates thesub-channel 1805 to the client station STA2 during the frame exchange1821.

FIG. 19 is a frame exchange 1900 between an AP and a plurality of clientstations STA0 and STA2 that includes downlink OFDMA transmission of datafrom the AP to the plurality client stations STA0 and STA2, according toan embodiment. In some embodiments, the AP 14 determines whethersub-channels allocated for a downlink OFDMA transmission are busy priorto the transmission. The frame exchange 1900 is generally similar to theframe exchange 1800, except that the AP 14 determines that a sub-channel1901 is busy, for example, as described above with respect to FIG. 14.The AP 14 transmits a downlink OFDMA data unit 1902 that omits an OFDMdata unit on the sub-channel 1901 during the frame exchange 1900. Insome embodiments, the AP 14 does not send downlink OFDM data units onthe sub-channel 1901 (e.g., the busy sub-channels) for the remainder ofthe TXOP.

While an 80 MHz communication channel is allocated to the clientstations in the illustrated embodiment of FIG. 19, the AP 14 selectsother sub-channel allocations (e.g., 60 MHz, 100 MHz, 120 MHz, 140 MHz,etc.) in other embodiments and/or scenarios. In an embodiment, the AP 14selects contiguous blocks of 40 MHz, 80 MHz, or 160 MHz for an uplinkMU-MIMO transmission. In some embodiments, a physical layer clearchannel assessment (PHY-CCA) provides an idle/busy indication for each20 MHz sub-channel of a communication channel. In an embodiment, thePHY-CCA is redefined to provide at least some sub-channel allocations.

FIG. 20 is a frame exchange 2000 between an AP 14 and a plurality ofclient stations STA0 and STA1 that includes downlink OFDMA transmissionof data from the AP to the plurality client stations STA0 and STA1,according to an embodiment. The frame exchange 2000 is generally similarto the frame exchange 1900, except that the AP 14 determines that asub-channel 2001 is busy, for example, as described above with respectto FIG. 14. The AP 14 transmits a downlink OFDMA data unit 2002 thatomits an OFDM data unit on the highest sub-channel 2001 during the frameexchange 1900. In some embodiments, the AP 14 does not send downlinkOFDM data units on the sub-channel 2001 (e.g., the busy sub-channels)for the remainder of the TXOP. In the embodiment shown in FIG. 20, thehighest 20 MHz sub-channel of the 80 MHz channel is determined to bebusy, the second highest 20 MHz sub-channel is allocated to the clientstation STA1, and a 40 MHz sub-channel that includes the second lowest20 MHz sub-channel and the lowest 20 MHz sub-channel is allocated toSTA0.

FIG. 21 is a frame exchange 2100 between an AP 14 and a plurality ofclient stations STA0 and STA2 that includes downlink OFDMA transmissionof data from the AP 14 to the plurality client stations STA0 and STA2,according to an embodiment. The frame exchange 2100 is generally similarto the frame exchange 2000, except that the AP 14 determines that aprimary sub-channel 2101 of a communication channel is busy during ascheduled service period, for example, as described above with respectto FIG. 14. In an embodiment, the AP 14 determines an availability ofthe sub-channel 2101 of the communication channel during the scheduledservice period based on an idle state during a point coordinationfunction interframe space (PIFS).

FIG. 22 is a frame exchange 2200 between an AP 14 and a plurality ofclient stations STA1, STA2, and STA3 that includes uplink OFDMAtransmission of data with selected traffic identifiers, according to anembodiment. The frame exchange 2200 is generally similar to the frameexchange 900, except that the AP 14 selects a traffic class (TC) and/oran access category (AC) for A-MPDUs, in an embodiment. The frameexchange 2200 includes a scheduling frame 2202, an uplink OFDMA dataunit 2204, and a block acknowledgment 2206. In various embodimentsand/or scenarios, different stations transmit uplink OFDM data unitshaving different traffic classes and/or access categories within a sameuplink transmission. In an embodiment, the AP 14 selects data frameswith a same access category to be encapsulated within an A-MPDU.

In some embodiments, the AP 14 selects a primary access category ortraffic class (e.g., a primary AC/TC) for each client station andprovides an indication of the selected AC/TC within the scheduling frame2202. In an embodiment, the indication of the selected AC/TC is includedin a PHY SIG field or a control frame. In an embodiment, for example,the scheduling frame 2202 includes i) an identifier for each of theclient stations STA1, STA2, and STA3, ii) an indication of sub-channelson which each client station should transmit for the OFDMA data unit2204, and iii) an indication of a traffic identifier that corresponds tothe primary AC/TC. In some embodiments, each client station has adifferent traffic identifier, for example, the AP 14 selects trafficidentifiers TID1, TID3, and TID5 for the client stations STA1, STA2, andSTA3, respectively. In an embodiment, this TC allocation is used in anuplink OFDMA exchange in a scheduled service period (TWT service period)and EDCA TXOP. In some embodiments, all client stations have a sametraffic identifier, for example, the AP 14 selects traffic identifiersTID1 for the client stations STA1, STA2, and STA3. In one embodiment,this TC allocation is used in an uplink OFDMA exchange in an EDCA TXOP.

In an embodiment, the client station selects frames having the primaryAC/TC for transmission in the uplink OFDMA data unit 2204. In anembodiment, the client station selects frames from an AC/TC differentfrom the primary AC/TC if no frames from the primary AC/TC are available(e.g., buffered for transmission). In other embodiments, the schedulingframe 2202 does not include a primary AC/TC and the client stationselects the AC/TC for its own uplink OFDM data unit of the OFDMAtransmission 2204.

FIG. 23 is a frame exchange 2300 between an AP 14 and a plurality ofclient stations STA1, STA2, and STA3 that includes downlink OFDMAtransmission of data with selected traffic identifiers, according to anembodiment. The frame exchange 2300 is generally similar to the frameexchange 1700, except that the AP 14 selects a traffic class and/or anaccess category for A-MPDUs, in an embodiment. In an embodiment, the AP14 selects traffic identifiers TID0, TID7, and TID5 for the clientstations STA1, STA2, and STA3, respectively, and generates OFDM dataunits 2302-1, 2302-2, and 2302-3 having frames with the correspondingtraffic identifier. In an embodiment, this TC allocation is used in adownlink OFDMA exchange in a scheduled service period (TWT serviceperiod) and an EDCA TXOP. In some embodiments, all client stations havea same traffic identifier, for example, the AP 14 selects the trafficidentifier TID1 for the client stations STA1, STA2, and STA3. In oneembodiment, this TC allocation is used in a downlink OFDMA exchange inan EDCA TXOP.

FIG. 24 is a frame exchange 2400 between an AP 14 and a plurality ofclient stations STA1, STA2, and STA3 that includes both uplink OFDMAtransmission of data and downlink OFDMA transmission of data withselected traffic identifiers, according to an embodiment. In someembodiments, the AP 14 provides an indication of different trafficclasses for both downlink OFDMA data units and uplink OFDMA data unitswithin a same TXOP. In the embodiment shown in FIG. 24, the frameexchange 2400 includes a downlink OFDMA data unit 2402, an uplink OFDMAdata unit 2404, and a block acknowledgment 2406. In an embodiment, theAP 14 generates the OFDMA data unit 2402 to include i) an A-MPDU havinga primary AC/TC for each client station, as described above with respectto FIG. 23, and ii) an indication of a primary AC/TC for a subsequentOFDMA transmission by each client station. In an embodiment, each clientstation generates an OFDM data unit of the uplink OFDMA data unit 2404to include MPDUs having the primary AC/TC indicated by the OFDMA dataunit 2402. In an embodiment, the AP 14 selects a first primary AC/TC forthe downlink OFDMA data unit 2402 and a second primary AC/TC for theuplink OFDMA data unit 2404 where the first primary AC/TC is differentfrom the second primary AC/TC.

FIG. 25 is a diagram illustrating example uplink OFDMA parameters 2500for an OFDMA group of client stations, and communications between an APand client stations of the OFDMA group that occur during time periodsdefined by the OFDMA parameters, according to an embodiment. The exampleuplink OFDMA parameters 1500 in FIG. 25 include a start time parameter1502 that indicates a start of communications between the AP 14 and theclient stations 25 of the OFDMA group, a service period 2504 thatdefines a time duration of communications between the AP 14 and theclient stations 25 of the OFDMA group, and a scheduling interval 2506that defines an interval between two consecutive service periods forcommunications between the AP 14 and the client stations 25 of the OFDMAgroup. In the embodiment of FIG. 25, the service period 2504 includes aframe exchange between the AP 14 and the client stations 25 in the OFDMAgroup, in which an uplink OFDMA data unit is transmitted from the clientstations 25 in the OFDMA group to the AP 14. For example, the serviceperiod 2504 includes the frame exchange 900 of FIG. 9 or anothersuitable frame exchange as described herein, in an embodiment. Invarious embodiments and/or scenarios, at the beginning of a scheduledservice period, the AP starts a downlink OFDMA frame exchange or uplinkframe exchange if the AP 14 determines that the medium is idle for PIFSor after a backoff procedure specific to the scheduled service period.

FIG. 26 is a flow diagram 2600 of an example method for simultaneouscommunication with multiple communication devices in a wireless localarea network, according to an embodiment. In an embodiment, the method2600 is implemented by an AP in the WLAN, according to an embodiment.With reference to FIG. 1, the method 2600 is implemented by the networkinterface 16 of the AP 14. For example, the method 2600 is implementedby the MAC processing unit 18 and/or by the PHY processing unit 20 ofthe network interface 16, in an embodiment. In other embodiments, themethod 2600 is implemented by other components of the AP 14, or isimplemented by a suitable communication device other than the AP 14.

At block 2602, respective sub-channels of an orthogonal frequencydivision multiplexing (OFDM) communication channel are allocated to twoor more second communication devices for simultaneous OFDM transmissionto the two or more second communication devices. In an embodiment, afirst sub-channel is allocated to a first one of the two or more secondcommunication devices and a second sub-channel is allocated to a secondone of the two or more second communication devices.

At block 2604, respective downlink OFDM data units for the two or moresecond communication devices using the corresponding allocatedsub-channels are generated. At block 2606, the downlink OFDM data unitsare transmitted to the two or more second communication devices usingthe corresponding allocated sub-channels.

At block 2608, at least a first uplink OFDM data unit is received fromthe first one of the two or more second communication devices and asecond uplink OFDM data unit is received from the second one of the twoor more second communication devices. The first uplink OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first one of the twoor more second communication devices in response to the correspondingdownlink OFDM data unit. The second uplink OFDM data unit is transmittedfrom the second one of the two or more second communication devices viathe second sub-channel allocated to the second one of the two or moresecond communication devices in response to the corresponding downlinkOFDM data unit.

FIG. 27 is a flow diagram 2700 of an example method for simultaneouscommunication with multiple communication devices in a wireless localarea network, according to an embodiment. In an embodiment, the method2700 is implemented by a client station in the WLAN, according to anembodiment. With reference to FIG. 1, the method 2700 is implemented bythe host processor 26 of the client station 25-1. For example, themethod 2700 is implemented by the MAC processing unit 28 and/or by thePHY processing unit 29 of the network interface 27, in an embodiment. Inother embodiments, the method 2700 is implemented by other components ofthe AP 14, or is implemented by a suitable communication device otherthan the AP 14.

At block 2702, a downlink orthogonal frequency division multiplexing(OFDM) data unit is received by a first communication device from asecond communication device via an OFDM communication channel.

At block 2704, a sub-channel of the OFDM communication channel on whichthe downlink OFDM data unit was transmitted by the second communicationdevice is identified.

At block 2706, an uplink OFDM data unit to be transmitted via thesub-channel on which the downlink OFDM data unit was transmitted isgenerated by the first communication device in response to the downlinkOFDM data unit.

At block 2708, the uplink OFDM data unit is automatically transmitted tothe second communication device via the sub-channel on which thedownlink OFDM data unit was transmitted.

FIG. 28 is a flow diagram 2800 of an example method for simultaneouscommunication with multiple communication devices in a wireless localarea network, according to an embodiment. In an embodiment, the method2800 is implemented by a client station in the WLAN, according to anembodiment. With reference to FIG. 1, the method 2800 is implemented bythe host processor 26 of the client station 25-1. For example, themethod 2800 is implemented by the MAC processing unit 28 and/or by thePHY processing unit 29 of the network interface 27, in an embodiment. Inother embodiments, the method 2800 is implemented by other components ofthe AP 14, or is implemented by a suitable communication device otherthan the AP 14.

At block 2802, one or more downlink orthogonal frequency divisionmultiplexing (OFDM) data units are received by a first communicationdevice. The downlink OFDM data units are transmitted by a secondcommunication device via one or more respective sub-channels of an OFDMcommunication channel.

At block 2804, the one or more sub-channels of the OFDM communicationchannel on which the one or more downlink OFDMA data units weretransmitted are identified by the first communication device.

At block 2806, a determination is made whether each of the one or moresub-channels on which the one or more downlink OFDMA data units weretransmitted is busy. At block 2808, an uplink OFDM data unit isgenerated for each sub-channel determined to be not busy. At block 2810,each of the uplink OFDM data units is transmitted to the secondcommunication device via the corresponding sub-channel.

Further aspects of the present invention relate to one or more of thefollowing clauses.

In an embodiment, a method for simultaneous communication with multiplecommunication devices in a wireless local area network includes:allocating, by a first communication device, respective sub-channels ofan orthogonal frequency division multiplexing (OFDM) communicationchannel to two or more second communication devices for simultaneousOFDM transmission to the two or more second communication devices,including allocating a first sub-channel to a first one of the two ormore second communication devices and a second sub-channel to a secondone of the two or more second communication devices; generating, by thefirst communication device, respective downlink OFDM data units for thetwo or more second communication devices using the correspondingallocated sub-channels; transmitting, by the first communication device,the downlink OFDM data units to the two or more second communicationdevices using the corresponding allocated sub-channels; and receiving,at the first communication device, at least i) a first uplink OFDM dataunit transmitted by the first one of the two or more secondcommunication devices in response to the corresponding downlink OFDMdata unit and ii) a second uplink OFDM data unit transmitted by thesecond one of the two or more second communication devices in responseto the corresponding downlink OFDM data unit, wherein the first uplinkOFDM data unit is transmitted from the first one of the two or moresecond communication devices via the first sub-channel allocated to thefirst one of the two or more second communication devices and the seconduplink OFDM data unit is transmitted from the second one of the two ormore second communication devices via the second sub-channel allocatedto the second one of the two or more second communication devices.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The downlink OFDM data units include synchronization frames and theuplink OFDM data units include aggregate media access control protocoldata units (A-MPDUs).

The synchronization frames include respective quality of serviceindicators, and each of the A-MPDUs includes two or more frames havingthe corresponding quality of service indicator.

The downlink OFDM data units are A-MPDUs and the uplink OFDM data unitsare corresponding acknowledgments to the A-MPDUs.

Generating the downlink OFDM data units includes generating a downlinkorthogonal frequency division multiple access (OFDMA) data unit thatincludes the downlink OFDM data units for the two or more secondcommunication devices, and receiving the first uplink OFDM data unit andthe second uplink OFDM data unit includes receiving an uplink OFDMA dataunit that includes the first uplink OFDM data unit and the second uplinkOFDM data unit.

The OFDM communication channel includes a multiple input, multipleoutput (MIMO) communication channel. Transmitting the downlink OFDM dataunits to the two or more second communication devices includestransmitting the downlink OFDM data units via the MIMO communicationchannel, the first sub-channel corresponding to a first space timestream of the MIMO communication channel and the second sub-channelcorresponding to a second space time stream of the MIMO communicationchannel. Receiving the first uplink OFDM data unit and the second uplinkOFDM data unit includes receiving the first uplink OFDM data unit viathe first space time stream and receiving the second uplink OFDM dataunit via the second space time stream. The first uplink OFDM data unitand the second uplink OFDM data unit are transmitted simultaneously fromthe first one of the two or more second communication devices and thesecond one of the two or more second communication devices,respectively.

The method further includes: determining an availability of eachsub-channel of the OFDM communication channel based on an idle stateduring a point coordination function interframe space (PIFS), andselecting the sub-channels of the OFDM communication channel forallocation based on the determined idle state.

In another embodiment, a first communication device includes a networkinterface device configured to: allocate respective sub-channels of anorthogonal frequency division multiplexing (OFDM) communication channelto two or more second communication devices for simultaneous OFDMtransmission to the two or more second communication devices, thesub-channels including a first sub-channel allocated to a first one ofthe two or more second communication devices and a second sub-channelallocated to a second one of the two or more second communicationdevices, generate respective downlink OFDM data units for the two ormore second communication devices using the corresponding allocatedsub-channels, transmit the downlink OFDM data units to the two or moresecond communication devices using the corresponding allocatedsub-channels, and receive, in response to the downlink OFDM data units,at least a first uplink OFDM data unit from the first one of the two ormore second communication devices and a second uplink OFDM data unitfrom the second one of the two or more second communication devices,wherein the first uplink OFDM data unit is transmitted from the firstone of the two or more second communication devices via the firstsub-channel allocated to the first one of the two or more secondcommunication devices and the second uplink OFDM data unit istransmitted from the second one of the two or more second communicationdevices via the second sub-channel allocated to the second one of thetwo or more second communication devices.

The downlink OFDM data units include synchronization frames and theuplink OFDM data units include aggregate media access control protocoldata units (A-MPDUs).

The synchronization frames include respective quality of serviceindicators, and each of the A-MPDUs includes two or more frames havingthe corresponding quality of service indicator.

The downlink OFDM data units are A-MPDUs and the uplink OFDM data unitsare corresponding acknowledgments to the A-MPDUs.

The network interface is configured to: generate a downlink orthogonalfrequency division multiple access (OFDMA) data unit that includes thedownlink OFDM data units for the two or more second communicationdevices, and receive an uplink OFDMA data unit that includes the firstuplink OFDM data unit and the second uplink OFDM data unit.

The OFDM communication channel includes a multiple input, multipleoutput (MIMO) communication channel, and the network interface isconfigured to transmit the downlink OFDM data units via the MIMOcommunication channel, the first sub-channel corresponding to a firstspace time stream of the MIMO communication channel and the secondsub-channel corresponding to a second space time stream of the MIMOcommunication channel, and receive the first uplink OFDM data unit viathe first space time stream and the second uplink OFDM data unit via thesecond space time stream, and the first uplink OFDM data unit and thesecond uplink OFDM data unit are transmitted simultaneously from thefirst one of the two or more second communication devices and the secondone of the two or more second communication devices, respectively.

In an embodiment, a method for simultaneous communication with multiplecommunication devices in a wireless local area network includes:receiving, at a first communication device from a second communicationdevice, a downlink orthogonal frequency division multiplexing (OFDM)data unit via an OFDM communication channel, identifying, by the firstcommunication device, a sub-channel of the OFDM communication channel onwhich the downlink OFDM data unit was transmitted by the secondcommunication device, generating, by the first communication device inresponse to the downlink OFDM data unit, an uplink OFDM data unit to betransmitted via the sub-channel on which the downlink OFDM data unit wastransmitted, automatically transmitting the uplink OFDM data unit to thesecond communication device via the sub-channel on which the downlinkOFDM data unit was transmitted.

Automatically transmitting the uplink OFDM data unit includestransmitting the uplink OFDM data unit after a short interframe space(SIFS) time interval from receipt of the downlink OFDM data unit withoutdetermining whether the sub-channel is busy between the receipt of thedownlink OFDM data unit and the transmission of the uplink OFDM dataunit.

The downlink OFDM data unit includes a synchronization frame and theuplink OFDM data unit includes an aggregate media access controlprotocol data unit (A-MPDU).

The method further includes: receiving, at the first communicationdevice via the sub-channel on which the downlink OFDM data unit wastransmitted, a block acknowledgment that indicates receipt of the A-MPDUby the second communication device.

The method further includes receiving, at the first communicationdevice, a broadcast block acknowledgment having i) a first deviceidentifier corresponding to the first communication device, ii) one ormore other device identifiers corresponding to one or more othercommunication devices, iii) a first bitmap that indicates whether eachMPDU in the A-MPDU was successfully received by the second communicationdevice, and iv) one or more other bitmaps corresponding to the one ormore other communication devices.

The synchronization frame includes a quality of service indicator, andgenerating the uplink OFDM data unit includes generating the A-MPDU toinclude two or more MPDUs having the corresponding quality of serviceindicator.

The downlink OFDM data unit includes an A-MPDU and the uplink OFDM dataunit includes an acknowledgment to the A-MPDU.

The uplink OFDM data unit is a portion of an orthogonal frequencydivision multiple access (OFDMA) data unit.

The OFDM communication channel includes a MIMO communication channel andthe sub-channel includes a space time stream of the MIMO communicationchannel. Receiving the downlink OFDM data unit includes receiving thedownlink OFDM data unit via the space time stream.

In another embodiment, a first communication device includes a networkinterface device configured to: receive, from a second communicationdevice, a downlink orthogonal frequency division multiplexing (OFDM)data unit via an OFDM communication channel, identify a sub-channel ofthe OFDM communication channel on which the downlink OFDM data unit wastransmitted by the second communication device, generate, in response tothe downlink OFDM data unit, an uplink OFDM data unit to be transmittedvia the sub-channel on which the downlink OFDM data unit wastransmitted, and automatically transmit the uplink OFDM data unit to thesecond communication device via the sub-channel on which the downlinkOFDM data unit was transmitted.

The network interface is configured to automatically transmit the uplinkOFDM data unit a short interframe space (SIFS) time interval afterreceipt of the downlink OFDM data unit without determining whether thesub-channel is busy between the receipt of the downlink OFDM data unitand the transmission of the uplink OFDM data unit.

The downlink OFDM data unit includes a synchronization frame and theuplink OFDM data unit includes an aggregate media access controlprotocol data unit (A-MPDU).

The network interface is configured to receive, via the sub-channel onwhich the downlink OFDM data unit was transmitted, a blockacknowledgment that indicates receipt of the A-MPDU by the secondcommunication device.

The network interface is configured to receive a broadcast blockacknowledgment having i) a first device identifier corresponding to thefirst communication device, ii) one or more other device identifierscorresponding to one or more other communication devices, iii) a firstbitmap that indicates whether each MPDU in the A-MPDU was successfullyreceived by the second communication device, and iv) one or more otherbitmaps corresponding to the one or more other communication devices.

The synchronization frame includes a quality of service indicator, andthe network interface is configured to generate the A-MPDU to includetwo or more MPDUs having the corresponding quality of service indicator.

The downlink OFDM data unit includes an A-MPDU and the uplink OFDM dataunit includes an acknowledgment to the A-MPDU.

The uplink OFDM data unit is a portion of an orthogonal frequencydivision multiple access (OFDMA) data unit, and wherein the OFDMA dataunit further includes another OFDM data unit simultaneously transmittedby a third communication device with the uplink OFDM data unit.

The OFDM communication channel includes a MIMO communication channel andthe sub-channel includes a space time stream of the MIMO communicationchannel. The network interface is configured to receive the downlinkOFDM data unit via the space time stream.

In an embodiment, a method for simultaneous communication with multiplecommunication devices in a wireless local area network includes:receiving, at a first communication device, one or more downlinkorthogonal frequency division multiplexing (OFDM) data units transmittedby a second communication device via one or more respective sub-channelsof an OFDM communication channel; identifying, by the firstcommunication device, the one or more sub-channels of the OFDMcommunication channel on which the one or more downlink OFDMA data unitswere transmitted; determining, by the first communication device,whether each of the one or more sub-channels on which the one or moredownlink OFDMA data units were transmitted is busy; generating, by thefirst communication device, an uplink OFDM data unit for eachsub-channel determined to be not busy; and transmitting each of theuplink OFDM data units to the second communication device via thecorresponding sub-channel.

The one or more downlink OFDM data units include synchronization framesand the one or more uplink OFDM data units include one or more aggregatemedia access control protocol data units (A-MPDU).

The method further includes: receiving, at the first communicationdevice via the sub-channels on which the one or more uplink OFDM dataunits were transmitted, a block acknowledgment that indicates receipt ofthe one or more A-MPDUs by the second communication device.

The method further includes: receiving, at the first communicationdevice, a broadcast block acknowledgment having i) a first deviceidentifier corresponding to the first communication device, ii) one ormore other device identifiers corresponding to one or more othercommunication devices, iii) one or more bitmaps that indicate whethereach of the one or more A-MPDUs was successfully received by the secondcommunication device, and iv) one or more other bitmaps corresponding tothe one or more other communication devices.

The synchronization frame includes a quality of service indicator, andgenerating the one or more uplink OFDM data units includes generatingthe one or more A-MPDU to include only MPDUs having the correspondingquality of service indicator.

The one or more downlink OFDM data units include one or more A-MPDUs andthe one or more uplink OFDM data units include one or moreacknowledgments to the one or more A-MPDU.

The one or more uplink OFDM data units are a portion of an orthogonalfrequency division multiple access (OFDMA) data unit.

The OFDM communication channel includes a MIMO communication channel andthe one or more sub-channels include one or more space time streams ofthe MIMO communication channel. Receiving the one or more downlink OFDMdata units includes receiving the one or more downlink OFDM data unitvia the corresponding space time stream.

In another embodiment, a first communication device includes a networkinterface device configured to: receive, from a second communicationdevice, one or more downlink orthogonal frequency division multiplexing(OFDM) data units transmitted by a second communication device via oneor more respective sub-channels of an OFDM communication channel,identify, by the first communication device, the one or moresub-channels of the OFDM communication channel on which the one or moredownlink OFDMA data units were transmitted, determine, by the firstcommunication device, whether each of the one or more sub-channels onwhich the one or more downlink OFDMA data units were transmitted isbusy; generate, by the first communication device, an uplink OFDM dataunit for each sub-channel determined to be not busy, and transmit eachof the uplink OFDM data units to the second communication device via thecorresponding sub-channel.

The one or more downlink OFDM data units include one or moresynchronization frames and the one or more uplink OFDM data unitsinclude one or more aggregate media access control protocol data units(A-MPDU).

The network interface is configured to receive, via the sub-channels onwhich the one or more uplink OFDM data units were transmitted, a blockacknowledgment that indicates receipt of the one or more A-MPDUs by thesecond communication device.

The network interface is configured to receive a broadcast blockacknowledgment having i) a first device identifier corresponding to thefirst communication device, ii) one or more other device identifierscorresponding to one or more other communication devices, iii) one ormore bitmaps that indicate whether each of the one or more A-MPDUs wassuccessfully received by the second communication device, and iv) one ormore other bitmaps corresponding to the one or more other communicationdevices.

The synchronization frame includes a quality of service indicator, andthe network interface is configured to generate the one or more uplinkOFDM data units includes generating the one or more A-MPDU to includeonly MPDUs having the corresponding quality of service indicator.

The one or more downlink OFDM data units include one or more A-MPDUs andthe one or more uplink OFDM data units include one or moreacknowledgments to the one or more A-MPDU.

The one or more uplink OFDM data units are a portion of an orthogonalfrequency division multiple access (OFDMA) data unit.

The OFDM communication channel includes a MIMO communication channel andthe one or more sub-channels include one or more space time streams ofthe MIMO communication channel. The network interface is configured toreceive the one or more downlink OFDM data unit via the correspondingspace time stream.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any tangible, non-transitorycomputer readable memory such as a magnetic disk, an optical disk, aRAM, a ROM, a flash memory, a tape drive, etc. The software or firmwareinstructions may include machine readable instructions that, whenexecuted by one or more processors, cause one or more processors toperform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, one or more integrated circuits, anapplication-specific integrated circuit (ASIC), a programmable logicdevice (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

1. A method for simultaneous communication with multiple communicationdevices in a wireless local area network, the method comprising:allocating, by a first communication device, respective sub-channels ofan orthogonal frequency division multiplexing (OFDM) communicationchannel to two or more second communication devices for simultaneousOFDM transmission to the two or more second communication devices,including allocating a first sub-channel to a first one of the two ormore second communication devices and a second sub-channel to a secondone of the two or more second communication devices; generating, by thefirst communication device, respective downlink OFDM data units for thetwo or more second communication devices using the correspondingallocated sub-channels; transmitting, by the first communication device,the downlink OFDM data units to the two or more second communicationdevices using the corresponding allocated sub-channels; and receiving,at the first communication device, at least i) a first uplink OFDM dataunit transmitted by the first one of the two or more secondcommunication devices in response to the corresponding downlink OFDMdata unit and ii) a second uplink OFDM data unit transmitted by thesecond one of the two or more second communication devices in responseto the corresponding downlink OFDM data unit, wherein the first uplinkOFDM data unit is transmitted from the first one of the two or moresecond communication devices via the first sub-channel allocated to thefirst one of the two or more second communication devices and the seconduplink OFDM data unit is transmitted from the second one of the two ormore second communication devices via the second sub-channel allocatedto the second one of the two or more second communication devices. 2.The method of claim 1, wherein: transmitting the downlink OFDM dataunits comprises performing a medium access procedure; and the downlinkOFDM data units and the uplink OFDM data units comprise respectivequality of service indicators selected based on the medium accessprocedure.
 3. The method of claim 1, wherein the downlink OFDM dataunits comprise synchronization frames and the uplink OFDM data unitscomprise aggregate media access control protocol data units (A-MPDUs).4. The method of claim 3, wherein: the synchronization frames includerespective quality of service indicators, and each of the A-MPDUscomprises two or more MPDUs having the corresponding quality of serviceindicator.
 5. The method of claim 4, wherein each of the A-MPDUs is anacknowledgement of the corresponding synchronization frame and receiptof at least one of the A-MPDUs indicates a successful frame exchange. 6.The method of claim 1, wherein the downlink OFDM data units are A-MPDUsand the uplink OFDM data units are corresponding acknowledgments to theA-MPDUs.
 7. The method of claim 1, wherein: generating the downlink OFDMdata units comprises generating a downlink orthogonal frequency divisionmultiple access (OFDMA) data unit that includes the downlink OFDM dataunits for the two or more second communication devices, and receivingthe first uplink OFDM data unit and the second uplink OFDM data unitcomprises receiving an uplink OFDMA data unit that includes the firstuplink OFDM data unit and the second uplink OFDM data unit.
 8. Themethod of claim 7, wherein: a total bandwidth of the uplink OFDMA dataunit corresponds to a total bandwidth of the downlink OFDMA data unit,each sub-channel of the uplink OFDMA data unit corresponds to asub-channel of the downlink OFDMA data unit, and each smallest bandwidthsub-channel of the OFDM communication channel occupied by the downlinkOFDMA data unit is occupied by at least one sub-channel of the uplinkOFDMA data unit.
 9. The method of claim 1, wherein: the OFDMcommunication channel comprises a multiple input, multiple output (MIMO)communication channel, transmitting the downlink OFDM data units to thetwo or more second communication devices comprises transmitting thedownlink OFDM data units via the MIMO communication channel, the firstsub-channel corresponding to a first space time stream of the MIMOcommunication channel and the second sub-channel corresponding to asecond space time stream of the MIMO communication channel, receivingthe first uplink OFDM data unit and the second uplink OFDM data unitcomprises receiving the first uplink OFDM data unit via the first spacetime stream and receiving the second uplink OFDM data unit via thesecond space time stream; and the first uplink OFDM data unit and thesecond uplink OFDM data unit are transmitted simultaneously from thefirst one of the two or more second communication devices and the secondone of the two or more second communication devices, respectively. 10.The method of claim 1, further comprising: determining an availabilityof each sub-channel of the OFDM communication channel based on an idlestate during a point coordination function interframe space (PIFS), andselecting the sub-channels of the OFDM communication channel forallocation based on the determined idle state.
 11. A first communicationdevice, comprising: a network interface configured to allocaterespective sub-channels of an orthogonal frequency division multiplexing(OFDM) communication channel to two or more second communication devicesfor simultaneous OFDM transmission to the two or more secondcommunication devices, the sub-channels including a first sub-channelallocated to a first one of the two or more second communication devicesand a second sub-channel allocated to a second one of the two or moresecond communication devices, generate respective downlink OFDM dataunits for the two or more second communication devices using thecorresponding allocated sub-channels, transmit the downlink OFDM dataunits to the two or more second communication devices using thecorresponding allocated sub-channels, and receive, in response to thedownlink OFDM data units, at least a first uplink OFDM data unit fromthe first one of the two or more second communication devices and asecond uplink OFDM data unit from the second one of the two or moresecond communication devices, wherein the first uplink OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first one of the twoor more second communication devices and the second uplink OFDM dataunit is transmitted from the second one of the two or more secondcommunication devices via the second sub-channel allocated to the secondone of the two or more second communication devices.
 12. The firstcommunication device of claim 11, wherein: the network interface isconfigured to perform a medium access procedure; and the downlink OFDMdata units and the uplink OFDM data units comprise respective quality ofservice indicators selected based on the medium access procedure. 13.The first communication device of claim 11, wherein the downlink OFDMdata units comprise synchronization frames and the uplink OFDM dataunits comprise aggregate media access control protocol data units(A-MPDUs).
 14. The first communication device of claim 9, wherein: thesynchronization frames include respective quality of service indicators,and each of the A-MPDUs comprises two or more MPDUs having thecorresponding quality of service indicator.
 15. The first communicationdevice of claim 14, wherein each of the A-MPDUs is an acknowledgement ofthe corresponding synchronization frame and receipt of at least one ofthe A-MPDUs indicates a successful frame exchange.
 16. The firstcommunication device of claim 11, wherein the downlink OFDM data unitsare A-MPDUs and the uplink OFDM data units are correspondingacknowledgments to the A-MPDUs.
 17. The first communication device ofclaim 11, wherein the network interface is configured to: generate adownlink orthogonal frequency division multiple access (OFDMA) data unitthat includes the downlink OFDM data units for the two or more secondcommunication devices, and receive an uplink OFDMA data unit thatincludes the first uplink OFDM data unit and the second uplink OFDM dataunit.
 18. The first communication device of claim 17, wherein: a totalbandwidth of the uplink OFDMA data unit corresponds to a total bandwidthof the downlink OFDMA data unit, each sub-channel of the uplink OFDMAdata unit corresponds to a sub-channel of the downlink OFDMA data unit,and each smallest bandwidth sub-channel of the OFDM communicationchannel occupied by the downlink OFDMA data unit is occupied by at leastone sub-channel of the uplink OFDMA data unit.
 19. The firstcommunication device of claim 11, wherein: the OFDM communicationchannel comprises a multiple input, multiple output (MIMO) communicationchannel, and the network interface is configured to transmit thedownlink OFDM data units via the MIMO communication channel, the firstsub-channel corresponding to a first space time stream of the MIMOcommunication channel and the second sub-channel corresponding to asecond space time stream of the MIMO communication channel, and receivethe first uplink OFDM data unit via the first space time stream and thesecond uplink OFDM data unit via the second space time stream, and thefirst uplink OFDM data unit and the second uplink OFDM data unit aretransmitted simultaneously from the first one of the two or more secondcommunication devices and the second one of the two or more secondcommunication devices, respectively.
 20. A method for simultaneouscommunication with multiple communication devices in a wireless localarea network, the method comprising: receiving, at a first communicationdevice from a second communication device, a downlink orthogonalfrequency division multiplexing (OFDM) data unit via an OFDMcommunication channel, identifying, by the first communication device, asub-channel of the OFDM communication channel on which the downlink OFDMdata unit was transmitted by the second communication device,generating, by the first communication device in response to thedownlink OFDM data unit, an uplink OFDM data unit to be transmitted viathe sub-channel on which the downlink OFDM data unit was transmitted,automatically transmitting the uplink OFDM data unit to the secondcommunication device via the sub-channel on which the downlink OFDM dataunit was transmitted.
 21. The method of claim 20, wherein automaticallytransmitting the uplink OFDM data unit comprises transmitting the uplinkOFDM data unit after a short interframe space (SIFS) time interval fromreceipt of the downlink OFDM data unit without determining whether thesub-channel is busy between the receipt of the downlink OFDM data unitand the transmission of the uplink OFDM data unit.
 22. The method ofclaim 21, wherein the downlink OFDM data unit comprises asynchronization frame and the uplink OFDM data unit comprises anaggregate media access control protocol data unit (A-MPDU).
 23. Themethod of claim 22, further comprising receiving, at the firstcommunication device via the sub-channel on which the downlink OFDM dataunit was transmitted, a block acknowledgment that indicates receipt ofthe A-MPDU by the second communication device.
 24. The method of claim22, further comprising receiving, at the first communication device, abroadcast block acknowledgment having i) a first device identifiercorresponding to the first communication device, ii) one or more otherdevice identifiers corresponding to one or more other communicationdevices, iii) a first bitmap that indicates whether each MPDU in theA-MPDU was successfully received by the second communication device, andiv) one or more other bitmaps corresponding to the one or more othercommunication devices.
 25. The method of claim 22, wherein: thesynchronization frame includes a quality of service indicator, andgenerating the uplink OFDM data unit comprises generating the A-MPDU toinclude two or more MPDUs having the corresponding quality of serviceindicator.
 26. The method of claim 20, wherein the downlink OFDM dataunit comprises an A-MPDU and the uplink OFDM data unit comprises anacknowledgment to the A-MPDU.
 27. The method of claim 20, wherein theuplink OFDM data unit is a portion of an orthogonal frequency divisionmultiple access (OFDMA) data unit.
 28. The method of claim 20, wherein:the OFDM communication channel comprises a MIMO communication channeland the sub-channel comprises a space time stream of the MIMOcommunication channel; receiving the downlink OFDM data unit comprisesreceiving the downlink OFDM data unit via the space time stream.
 29. Afirst communication device, comprising: a network interface configuredto receive, from a second communication device, a downlink orthogonalfrequency division multiplexing (OFDM) data unit via an OFDMcommunication channel, identify a sub-channel of the OFDM communicationchannel on which the downlink OFDM data unit was transmitted by thesecond communication device, generate, in response to the downlink OFDMdata unit, an uplink OFDM data unit to be transmitted via thesub-channel on which the downlink OFDM data unit was transmitted, andautomatically transmit the uplink OFDM data unit to the secondcommunication device via the sub-channel on which the downlink OFDM dataunit was transmitted.
 30. The first communication device of claim 29,wherein the network interface is configured to automatically transmitthe uplink OFDM data unit a short interframe space (SIFS) time intervalafter receipt of the downlink OFDM data unit without determining whetherthe sub-channel is busy between the receipt of the downlink OFDM dataunit and the transmission of the uplink OFDM data unit.
 31. The firstcommunication device of claim 30, wherein the downlink OFDM data unitcomprises a synchronization frame and the uplink OFDM data unitcomprises an aggregate media access control protocol data unit (A-MPDU).32. The first communication device of claim 31, wherein the networkinterface is configured to receive, via the sub-channel on which thedownlink OFDM data unit was transmitted, a block acknowledgment thatindicates receipt of the A-MPDU by the second communication device. 33.The first communication device of claim 30, wherein the networkinterface is configured to receive a broadcast block acknowledgmenthaving i) a first device identifier corresponding to the firstcommunication device, ii) one or more other device identifierscorresponding to one or more other communication devices, iii) a firstbitmap that indicates whether each MPDU in the A-MPDU was successfullyreceived by the second communication device, and iv) one or more otherbitmaps corresponding to the one or more other communication devices.34. The first communication device of claim 30, wherein: thesynchronization frame includes a quality of service indicator, and thenetwork interface is configured to generate the A-MPDU to include two ormore MPDUs having the corresponding quality of service indicator. 35.The first communication device of claim 29, wherein the downlink OFDMdata unit comprises an A-MPDU and the uplink OFDM data unit comprises anacknowledgment to the A-MPDU.
 36. The first communication device ofclaim 29, wherein the uplink OFDM data unit is a portion of anorthogonal frequency division multiple access (OFDMA) data unit, andwherein the OFDMA data unit further comprises another OFDM data unitsimultaneously transmitted by a third communication device with theuplink OFDM data unit.
 37. The first communication device of claim 29,wherein: the OFDM communication channel comprises a MIMO communicationchannel and the sub-channel comprises a space time stream of the MIMOcommunication channel; and the network interface is configured toreceive the downlink OFDM data unit via the space time stream. 38.-53.(canceled)